全文获取类型
收费全文 | 7629篇 |
免费 | 663篇 |
国内免费 | 4篇 |
专业分类
8296篇 |
出版年
2023年 | 58篇 |
2022年 | 142篇 |
2021年 | 273篇 |
2020年 | 147篇 |
2019年 | 176篇 |
2018年 | 199篇 |
2017年 | 160篇 |
2016年 | 335篇 |
2015年 | 510篇 |
2014年 | 521篇 |
2013年 | 533篇 |
2012年 | 755篇 |
2011年 | 648篇 |
2010年 | 375篇 |
2009年 | 364篇 |
2008年 | 490篇 |
2007年 | 424篇 |
2006年 | 380篇 |
2005年 | 290篇 |
2004年 | 288篇 |
2003年 | 262篇 |
2002年 | 244篇 |
2001年 | 55篇 |
2000年 | 32篇 |
1999年 | 38篇 |
1998年 | 60篇 |
1997年 | 30篇 |
1996年 | 22篇 |
1995年 | 30篇 |
1994年 | 23篇 |
1993年 | 27篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 27篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 22篇 |
1983年 | 29篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 13篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1974年 | 12篇 |
1973年 | 10篇 |
排序方式: 共有8296条查询结果,搜索用时 15 毫秒
61.
62.
Kozma N Halasz M Polgar B Poehlmann TG Markert UR Palkovics T Keszei M Par G Kiss K Szeberenyi J Grama L Szekeres-Bartho J 《Journal of immunology (Baltimore, Md. : 1950)》2006,176(2):819-826
Progesterone-induced blocking factor (PIBF) induces Th2-dominant cytokine production. Western blotting and EMSA revealed phosphorylation as well as nuclear translocation of STAT6 and inhibition of STAT4 phosphorylation in PIBF-treated cells. The silencing of STAT6 by small interfering RNA reduced the cytokine effects. Because the activation of the STAT6 pathway depends on the ligation of IL-4R, we tested the involvement of IL-4R in PIBF-induced STAT6 activation. Although PIBF does not bind to IL-4R, the blocking of the latter with an Ab abolished PIBF-induced STAT6 activation, whereas the blocking of the IL-13R had no effect. PIBF activated suppressor of cytokine signaling-3 and inhibited IL-12-induced suppressor of cytokine signaling-1 activation. The blocking of IL-4R counteracted all the described effects, suggesting that the PIBF receptor interacts with IL-4R alpha-chain, allowing PIBF to activate the STAT6 pathway. PIBF did not phosphorylate Jak3, suggesting that the gamma-chain is not needed for PIBF signaling. Confocal microscopic analysis revealed a colocalization and at 37 degrees C a cocapping of the FITC PIBF-activated PIBF receptor and PE anti-IL-4R-labeled IL-4R. After the digestion of the cells with phosphatidylinositol-specific phospholipase C, the STAT6-activating effect of PIBF was lost, whereas that of IL-4 remained unaltered. These data suggest the existence of a novel type of IL-4R composed of the IL-4R alpha-chain and the GPI-anchored PIBF receptor. 相似文献
63.
Gath J Habenstein B Bousset L Melki R Meier BH Böckmann A 《Biomolecular NMR assignments》2012,6(1):51-55
Parkinson’s disease is amongst the most frequent and most devastating neurodegenerative diseases. It is tightly associated
with the assembly of proteins into high-molecular weight protein species, which propagate between neurons in the central nervous
system. The principal protein involved in this process is α-synuclein which is a structural component of the Lewy bodies observed
in diseased brain. We here present the solid-state NMR sequential assignments of a new fibrillar form of this protein, the
first one with a well-ordered and rigid N-terminal part. 相似文献
64.
Julia F. Morton 《Economic botany》1991,45(3):318-333
The horseradish tree (Moringa pterygosperma,) is being introduced into drought-ridden lands to augment the local food and
fodder supply. The tree grows up to 5 m per year. The foliage is high in calcium and has half the oxalates of amaranth. Seeds
yield edible oil and the seed meal is used as fertilizer and as a coagulant to clarify turbid water. The philanthropic center,
ECHO (Educational Concerns for Hunger Organization), North Fort Myers, Florida, receives many requests for seeds. A missionary
in Mali wrote: “The seeds you sent arrived during the worst year of 14 years of dry weather. Only the moringa survived, and
they have flourished. ”Another seed shipment resulted, after harvesting a crop, in 25 000 trees being planted by university
students and faculty, around laborers’ houses in Maranhao, Brazil. The tree is not limited to tropical lowlands, but thrives
at elevations of 800-1200 m in protected mountain areas of southern Mexico. The long-range effects of ingesting various parts
of the tree as food or folkmedicine need study. Attention should be given to horticultural improvement, perhaps through hybridization
with one or more related species now being compared with M. pterygosperma in India and Africa.
ХРеНовое дерево, Moringa pterygosperma F. Gaertn. (Moringaceae), Дар сыхим землям. Хреновое дерево, Moringa pterygosperma,
вводится в бездождивые землии чтоб умножить местное снабжение пищи и корма. Дерево растет до 5 метров в год. Листья содержат
много кальцию и половину щавелев по сравнени#x044E; с амарантом. Семя дают съедобное масло и семеная мука употребляется как
одобрение и как коагулант для очищение мутной воды. Филантропический цэнтэр ECHO (Educational Concern for Hunger Organization,
North Fort Myers, Florida) полужает мното просьб чтоб получить семя. Один миссионер из Мали писал “Семя которые вы послали,
прибыли в самый сухой год за 14 лет сухой погоды. Только моринга пережила и цвела. Другая отправка семен была совершена после
получения урожая и 25000 деревьев были посажены студентами и учителями около домов рабочих в Маранхау, Брразилия.
Это дерево не ограаничевается тропическим климатом и преуспевает на уровне 800 до 1200 метров в защищенных горных местах южной
Мексики. 相似文献
65.
Yao‐Bin Liu Yogendra Kharode Peter V.N. Bodine Paul J. Yaworsky John A. Robinson Julia Billiard 《Journal of cellular biochemistry》2010,109(4):794-800
The bioactive phospholipid, lysophosphatidic acid (LPA), acting through at least five distinct receptors LPA1–LPA5, plays important roles in numerous biological processes. Here we report that LPA induces osteoblastic differentiation of human mesenchymal stem cells hMSC‐TERT. We find that hMSC‐TERT mostly express two LPA receptors, LPA1 and LPA4, and undergo osteoblastic differentiation in serum‐containing medium. Inhibition of LPA1 with Ki16425 completely abrogates osteogenesis, indicating that this process is mediated by LPA in the serum through activation of LPA1. In contrast to LPA1, down‐regulation of LPA4 expression with shRNA significantly increases osteogenesis, suggesting that this receptor normally exerts negative effects on differentiation. Mechanistically, we find that in hMSC‐TERT, LPA induces a rise in both cAMP and Ca2+. The rise in Ca2+ is completely abolished by Ki16425, whereas LPA‐mediated cAMP increase is not sensitive to Ki16425. To test if LPA signaling pathways controlling osteogenesis in vitro translate into animal physiology, we evaluated the bones of LPA4‐deficient mice. Consistent with the ability of LPA4 to inhibit osteoblastic differentiation of stem cells, LPA4‐deficient mice have increased trabecular bone volume, number, and thickness. J. Cell. Biochem. 109: 794–800, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
66.
Albert Flexas Jaume Rosselló Julia F. Christensen Marcos Nadal Antonio Olivera La Rosa Enric Munar 《PloS one》2013,8(11)
We examined the influence of affective priming on the appreciation of abstract artworks using an evaluative priming task. Facial primes (showing happiness, disgust or no emotion) were presented under brief (Stimulus Onset Asynchrony, SOA = 20ms) and extended (SOA = 300ms) conditions. Differences in aesthetic liking for abstract paintings depending on the emotion expressed in the preceding primes provided a measure of the priming effect. The results showed that, for the extended SOA, artworks were liked more when preceded by happiness primes and less when preceded by disgust primes. Facial expressions of happiness, though not of disgust, exerted similar effects in the brief SOA condition. Subjective measures and a forced-choice task revealed no evidence of prime awareness in the suboptimal condition. Our results are congruent with findings showing that the affective transfer elicited by priming biases evaluative judgments, extending previous research to the domain of aesthetic appreciation. 相似文献
67.
Michael J. J. Chu Anthony R. J. Phillips Alexander W. G. Hosking Julia R. MacDonald Adam S. J. R. Bartlett Anthony J. R. Hickey 《PloS one》2013,8(10)
Backgrounds and Aim
Current assessment of pre-operative liver function relies upon biochemical blood tests and histology but these only indirectly measure liver function. Mitochondrial function (MF) analysis allows direct measurement of cellular metabolic function and may provide an additional index of hepatic health. Conventional MF analysis requires substantial tissue samples (>100 mg) obtained at open surgery. Here we report a method to assess MF using <3 mg of tissue obtained by a Tru-cut® biopsy needle making it suitable for percutaneous application.Methods
An 18G Bard® Max-core® biopsy instrument was used to collect samples. The optimal Tru-cut® sample weight, stability in ice-cold University of Wisconsin solution, reproducibility and protocol utility was initially evaluated in Wistar rat livers then confirmed in human samples. MF was measured in saponin-permeabilized samples using high-resolution respirometry.Results
The average mass of a single rat and human liver Tru-cut® biopsy was 5.60±0.30 and 5.16±0.15 mg, respectively (mean; standard error of mean). Two milligram of sample was found the lowest feasible mass for the MF assay. Tissue MF declined after 1 hour of cold storage. Six replicate measurements within rats and humans (n = 6 each) showed low coefficient of variation (<10%) in measurements of State-III respiration, electron transport chain (ETC) capacity and respiratory control ratio (RCR). Ischemic rat and human liver samples consistently showed lower State-III respiration, ETC capacity and RCR, compared to normal perfused liver samples.Conclusion
Consistent measurement of liver MF and detection of derangement in a disease state was successfully demonstrated using less than half the tissue from a single Tru-cut® biopsy. Using this technique outpatient assessment of liver MF is now feasible, providing a new assay for the evaluation of hepatic function. 相似文献68.
Industrial emissions of SO2 and NOx, resulting in the formation and deposition of sulfuric and nitric acids, affect the health of both terrestrial and aquatic ecosystems. Since the mid-late 20th century, legislation to control acid rain precursors in both Europe and the US has led to significant declines in both SO4–S and H+ in precipitation and streams. However, several authors noted that declines in streamwater SO4–S did not result in stoichiometric reductions in stream H+, and suggested that observed reductions in base cation inputs in precipitation could lessen the effect of air pollution control on improving stream pH. We examined long-term precipitation chemistry (1978–2010) from nearly 30 sites in the US and Europe that are variably affected by acid deposition and that have a variety of industrial and land-use histories to (1) quantify trends in SO4–S, H+, NH4–N, Ca, and NO3–N, (2) assess stoichiometry between H+ and SO4–S before and after 1990, and (3) examine regional synchrony of trends. We expected that although the overall efforts of developed countries to reduce air pollution and acid rain by the mid-late 20th century would tend to synchronize precipitation chemistry among regions, geographically varied patterns of fossil fuel use and pollution control measures would produce important asynchronies among European countries and the United States. We also expected that control of particulate versus gaseous emission, along with trends in NH3 emissions, would be the two most significant factors affecting the stoichiometry between SO4–S and H+. Relationships among H+, SO4–S, NH4–N, and cations differed markedly between the US and Europe. Controlling for SO4–S levels, H+ in precipitation was significantly lower in Europe than in the US, because (1) alkaline dust loading from the Sahara/Sahel was greater in Europe than the US, and (2) emission of NH3, which neutralizes acidity upon conversion to NH4 +, is generally significantly higher in Europe than in the US. Trends in SO4–S and H+ in precipitation were close to stoichometric in the US throughout the period of record, but not in Europe, especially eastern Europe. Ca in precipitation declined significantly before, but not after 1990 in most of the US, but Ca declined in eastern Europe even after 1990. SO4–S in precipitation was only weakly related to fossil fuel consumption. The stoichiometry of SO4–S and H+ may be explained in part by emission controls, which varied over time and among regions. Control of particulate emissions reduces alkaline particles that neutralize acid precursors as well as S-containing particulates, reducing SO4–S and Ca more steeply than H+, consistent with trends in the northeastern US and Europe before 1990. In contrast, control of gaseous SO2 emissions results in a stoichiometric relationship between SO4–S and H+, consistent with trends in the US and many western European countries, especially after 1991. However, in many European countries, declining NH3 emissions contributed to the lack of stoichiometry between SO4–S and H+.Recent reductions in NOx emissions have also contributed to declines in H+ in precipitation. Future changes in precipitation acidity are likely to depend on multiple factors including trends in NOx and NH3 emission controls, naturally occurring dust, and fossil fuel use, with significant implications for the health of both terrestrial and aquatic ecosystems. 相似文献
69.
R. Ashton Lavoie Jeffrey T. Zugates Andrew T. Cheeseman Matt A. Teten Srivatsan Ramesh Julia M. Freeman Summer Swango Jeremy Fitzpatrick Amod Joshi Bradley Hollers Zufan Debebe Tyler K. Lindgren Amber N. Kozak Vinay K. Kondeti Mary K. Bright Eric J. Yearley Alexander Tracy Jacob A. Irwin Michael Guerrero 《Biotechnology and bioengineering》2023,120(10):2953-2968
Adeno-associated virus-based gene therapies have demonstrated substantial therapeutic benefit for the treatment of genetic disorders. In manufacturing processes, viral capsids are produced with and without the encapsidated gene of interest. Capsids devoid of the gene of interest, or “empty” capsids, represent a product-related impurity. As a result, a robust and scalable method to enrich full capsids is crucial to provide patients with as much potentially active product as possible. Anion exchange chromatography has emerged as a highly utilized method for full capsid enrichment across many serotypes due to its ease of use, robustness, and scalability. However, achieving sufficient resolution between the full and empty capsids is not trivial. In this work, anion exchange chromatography was used to achieve empty and full capsid resolution for adeno-associated virus serotype 5. A salt gradient screen of multiple salts with varied valency and Hofmeister series properties was performed to determine optimal peak resolution and aggregate reduction. Dual salt effects were evaluated on the same product and process attributes to identify any synergies with the use of mixed ion gradients. The modified process provided as high as ≥75% AAV5 full capsids (≥3-fold enrichment based on the percent full in the feed stream) with near baseline separation of empty capsids and achieved an overall vector genome step yield of >65%. 相似文献
70.
Free-living birds are often presented to veterinarians at rehabilitation centers as well as in private practice. Information about disease processes and causes of death of indigenous free-living birds can aid the clinician in establishing proper treatment and in the assessment of potential zoonotic risks. For the present study, pathogens as causes of morbidity and mortality were determined by performing a complete necropsy on free-living birds presented to the Clinic for Birds and Reptiles of the University of Leipzig (Germany) that died shortly after admission or were euthanized due to an unfavorable prognosis. Over a 2-year period, 251 birds representing 13 families (Accipitridae, Apodidae, Columbidae, Corvidae, Falconidae, Fringillidae, Hirundinidae, Paridae, Passeridae, Picidae, Strigidae, Sturnidae and Turdidae) were examined. Trauma (62%), including several bite injuries inducing bacterial septicemia caused by Pasteurella multocida, was the most common cause of morbidity. Parasitic disease (18%) was mainly caused by Trichomonas gallinae, Eucoleus dispar and Syngamus trachea. Metabolic disease (13%), including fibrous osteodystrophy, was almost exclusively limited to juvenile specimens. Different Enterobacteriaceae including E. coli, Salmonella Typhimurium DT040 as well as Mycobacterium avium ssp. avium were identified as causal agents of primary bacterial disease (5%). Primary bacterial infection as cause of death or disease was of major importance in nestlings. Viral infections, mycoses and intoxication had minor significance as causes of morbidity. 相似文献