全文获取类型
收费全文 | 3093篇 |
免费 | 260篇 |
国内免费 | 161篇 |
出版年
2024年 | 9篇 |
2023年 | 83篇 |
2022年 | 81篇 |
2021年 | 117篇 |
2020年 | 129篇 |
2019年 | 188篇 |
2018年 | 140篇 |
2017年 | 151篇 |
2016年 | 123篇 |
2015年 | 124篇 |
2014年 | 175篇 |
2013年 | 254篇 |
2012年 | 139篇 |
2011年 | 130篇 |
2010年 | 109篇 |
2009年 | 132篇 |
2008年 | 138篇 |
2007年 | 116篇 |
2006年 | 129篇 |
2005年 | 109篇 |
2004年 | 95篇 |
2003年 | 72篇 |
2002年 | 79篇 |
2001年 | 67篇 |
2000年 | 57篇 |
1999年 | 63篇 |
1998年 | 41篇 |
1997年 | 42篇 |
1996年 | 34篇 |
1995年 | 38篇 |
1994年 | 27篇 |
1993年 | 31篇 |
1992年 | 24篇 |
1991年 | 30篇 |
1990年 | 18篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 23篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 5篇 |
排序方式: 共有3514条查询结果,搜索用时 15 毫秒
41.
Haptoglobin (HP), transferrin (TF), group specific component (GC) and protease inhibitor (PI) polymorphisms were studied in
a population sample (n=272) from Tyrol (Austria). Comparing the allele frequencies of these polymorphic serum protein systems
with those reported on other Austrian population samples some heterogeneity in the regional distribution of allele frequencies
was seen, especially concerning the GC system. The reasons for that may be due to different historical backgrounds in the
various regions of Austria. 相似文献
42.
Low-humidity treatment triggered an increase of the thallus area and the chlorophyll content in the following high-humidity
condition. When low-humidity treatment for 4 days was intercalated in high-humidity conditions every 16 days, the thallus
area increased 40% in 76 days. 相似文献
43.
The growth of lichens in the field is slow and their cultivation is generally thought to be difficult. We studied the effects
of environmental conditions and culture solutions on the growth of a lichen, and found that growth ofParmotrema tinctorum (Nyl.) Hale in growth cabinets was possible. The thallus area increased by about 20% monthly when the lichen was soaked in
a culture solution for 90 min every four days and then grown at 100% relative humidity when the temperature in the growth
cabinet was 20C and illumination was at 12 W/m2 for 16 hr daily. 相似文献
44.
高苯丙氨酸血症大鼠脑内单胺类递质的研究 总被引:3,自引:0,他引:3
以3d龄Sprague-Dawley大鼠腹腔注射苯丙氨酸(Phe)诱导高苯丙氨酸血症,荧光法测定大脑皮层及其突触体中去甲肾上腺素(NE)、多巴胺(DA)和5-羟色胺(5-HT)含量;Y型电迷宫法测其学习记忆能力.结果显示:高苯丙氨酸血症大鼠大脑皮层NE、DA及5-HT含量降低38.6%~67.4%,突触体中NE、DA和5-HT含量降低51.9%~70.2%,学习记忆能力明显低于对照组.结果提示,苯酮尿症智力障碍可能与大脑皮层及其突触体中某些单胺类递质含量降低相关. 相似文献
45.
M A Campbell C J Handley V C Hascall R A Campbell D A Lowther 《Archives of biochemistry and biophysics》1984,234(1):275-289
Proteoglycans in cultures of adult bovine articular cartilage labeled with [35S]sulfate after 5 days in culture and maintained in medium containing 20% fetal calf X serum had longer half-lives (average 11 days) compared with those of the same tissue maintained in medium alone (average 6 days). The half-lives of proteoglycans in cultures of calf cartilage labeled after 5 days in culture and maintained in medium with serum were considerably longer (average 21 days) compared to adult cartilage. If 0.5 mM cycloheximide was added to the medium of cultures of adult cartilage, or the tissue was maintained at 4 degrees C after labeling, the half-lives of the proteoglycans were greater, 24 and greater than 300 days, respectively. Analyses of the radiolabeled proteoglycans remaining in the matrix of the tissue immediately after labeling the tissue and at various times in culture revealed two main populations of proteoglycans; a large species eluting with Kav of 0.21-0.24 on Sepharose CL-2B, of high bouyant density and able to form aggregates with hyaluronate, and a small species eluting with a Kav of 0.63-0.70 on Sepharose CL-2B, of low buoyant density, containing only chondroitin sulfate chains, and unable to form aggregates with hyaluronate. The larger proteoglycan had shorter half-lives than the smaller proteoglycan; in cartilage maintained with serum, the half-lives were 9.8 and 14.5 days, respectively. Labeling cartilage with both [3H]leucine and [35S]sulfate showed the small proteoglycan to be a separate synthetic product. The size distribution of 35S-labeled proteoglycans lost into the medium was shown to be polydisperse on Sepharose CL-2B, the majority eluting with a Kav of 0.27 to 0.35, of high buoyant density, and unable to aggregate with hyaluronate. The size distribution of glycosaminoglycans from 35S-labeled proteoglycans appearing in the medium did not differ from that associated with labeled proteoglycans remaining in the matrix. 相似文献
46.
Monosaccharides, disaccharides, and trisaccharides were tested as inhibitors of the in vitro growth of Plasmodium falciparum (strain FCB). While certain monosaccharides (N-acetyl-D-glucosamine, D-mannose, and 3-O-methyl-D-glucose) proved to exhibit a toxic or reversibly retarding effect on the intraerythrocytic development of the parasite, the corresponding alpha- or beta-methylglycosides did not. Several methylglycosides, synthetic di- and tri-saccharides, and artificial blood group antigens were further tested for inhibitory effects on invasion of host red blood cells in vitro. The synthetic disaccharides beta DGlcNAc(1----4) alpha DManOMe and beta DGlcNAc(1----4) DGlcNAc (chitobiose) were good inhibitors of invasion at 10 mM concentration, whereas beta DGal(1----4)beta DGlcNAcOMe was negligibly inhibitory. The inhibition rate of N-acetyl-D-glucosamine, beta-glycosidically linked to bovine serum albumin (BSA) by an alipathic spacer, -(CH2)8CO-, was not enhanced, compared to the corresponding hapten, beta DGlcNAcO(CH2)8COOCH3. The inhibition rates of blood group A- and B-trisaccharide haptens, which were inhibitors of invasion, were also not significantly enhanced when coupled to BSA by way of the corresponding amide spacer, -(CH2)2NHCO(CH2)7CO-. A remarkable enhancement of the inhibition rate was, however, observed when beta DGal(1----3) alpha DGalNAcO(CH2)2NHCO(CH2)7COOCH3 (T-hapten) was coupled to BSA. A clear-cut decrease in the inhibition rates of different beta-glycosides of N-acetyl-D-glucosamine, beta DGlcNAcOR, was observed, depending on the nature of the aglycon R(p-nitrophenyl greater than -(CH2)8COOCH3 greater than -(CH2)2NHCO(CH2)2COOCH3 greater than -CH3). Also, p-nitrophenyl-alpha-D-glucopyranoside was a much better inhibitor of invasion than the corresponding methyl glycoside, alpha DGlcOMe, which was not inhibitory. The properties of the aglycon spacer, used for the covalent attachment of the carbohydrate to the carrier protein, may thus be crucial for the outcome of the inhibition rate. 相似文献
47.
Summary Three cultivation systems were compared. In one system the alders were grown hydroponically. In the two other systems the alders were planted in gravel and either given water and nutrients at intervals or the nutrient solution was continuously supplied. Alders continuously supplied with nutrients and water showed a significantly more rapid growth, higher biomass production and higher nitrogen content than did alders given nutrients and water at intervals or alders hydroponically grown. Alders continuously supplied with water and nutrients had a constant RE (relative efficiency of nitrogenase) of about 0.80 throughout the experimental period while alders supplied with water and nutrients at intervals showed a slight decrease in RE at the end of the experimental period. No strict relationship was found between RE and nitrogen content or between RE and plant productivity. 相似文献
48.
The morphology ofPedobesia lamourouxii andDerbesia ryukyuensis, both collected in Shimoda and the adjacent areas in central Japan, was studied from field specimens and laboratory cultures.
Specimens which had the same morphology as EuropeanP. lamourouxii produced stephanokont zoospores which developed into either prostrate filaments or expanded discoidal thalli similar to those
described by Feldmann and Codomier (1974) and Feldmannet al. (1975). Erect filament identical with the thallus found in nature developed directly from prostrate filaments. The specimens
which had morphology similar to that ofDerbesia ryukyuensis described by Yamada and Tanaka (1938) also produced stephanokont zoospores which developed similarly to those ofP. lamourouxii. This species is, therefore, a member ofPedobesia, and it is made a new combinationP. ryukyuensis (Yamada et Tanaka) Kobara et Chihara, comb. nov. 相似文献
49.
Bloodstream forms of Trypanosoma brucei that were infective for mammals, when grown in vitro at 37 C for 29 days or 25 months had amounts of variant surface glycoprotein similar to the amounts from bloodstream forms isolated from infected rat blood. The amounts were measured by competition radioimmunoassays for both unique and cross-reacting determinants and the results were the same, providing evidence that a single type of variant surface glycoprotein was measured. Neither radioimmunoassay detected determinants of variant surface glycoproteins in trypanosomes transformed by culturing at 27 C to insect forms not infective for mammals. 相似文献
50.
Summary In the rostral hypothalamus of the domestic fowl, the magnocellular neurosecretory nuclei show a peculiar differentiation. Golgi studies of the supraoptic and paraventricular nuclei of the fowl reveal at least two major cell types: 1) large multipolar neurons, and 2) small interneurons. Golgi impregnations provide a detailed cytoarchitectural picture of the large-sized cells; the latter may well correspond to the neurosecretory cells demonstrated in the same regions by selective staining, and immunocytochemical and electron microscopical techniques.Electron microscopically, neuronal perikarya are observed to contain variable amounts of neurosecretory granules (100–200 nm in diameter; mean diameter of 160 nm) scattered throughout the cytoplasm. The diameters of these granules do not differ statistically in the two principal nuclear areas examined. The perikarya of these neurons display only a few axosomatic synapses containing electron-lucent and dense-cored vesicles (70–90 nm in diameter). Numerous nerve terminals of this type also end on the dendritic ramifications in the surrounding neuropil. 相似文献