全文获取类型
收费全文 | 10203篇 |
免费 | 997篇 |
国内免费 | 11篇 |
出版年
2021年 | 121篇 |
2020年 | 51篇 |
2019年 | 90篇 |
2018年 | 84篇 |
2017年 | 84篇 |
2016年 | 143篇 |
2015年 | 299篇 |
2014年 | 306篇 |
2013年 | 430篇 |
2012年 | 611篇 |
2011年 | 574篇 |
2010年 | 423篇 |
2009年 | 362篇 |
2008年 | 545篇 |
2007年 | 587篇 |
2006年 | 526篇 |
2005年 | 603篇 |
2004年 | 620篇 |
2003年 | 591篇 |
2002年 | 545篇 |
2001年 | 110篇 |
2000年 | 68篇 |
1999年 | 130篇 |
1998年 | 181篇 |
1997年 | 106篇 |
1996年 | 117篇 |
1995年 | 116篇 |
1994年 | 116篇 |
1993年 | 95篇 |
1992年 | 114篇 |
1991年 | 91篇 |
1990年 | 95篇 |
1989年 | 81篇 |
1988年 | 88篇 |
1987年 | 83篇 |
1986年 | 78篇 |
1985年 | 95篇 |
1984年 | 130篇 |
1983年 | 109篇 |
1982年 | 134篇 |
1981年 | 142篇 |
1980年 | 115篇 |
1979年 | 81篇 |
1978年 | 93篇 |
1977年 | 87篇 |
1976年 | 84篇 |
1975年 | 89篇 |
1974年 | 83篇 |
1973年 | 95篇 |
1972年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Visser WF van Roermund CW Ijlst L Waterham HR Wanders RJ 《The Biochemical journal》2007,401(2):365-375
In recent years, much progress has been made with respect to the unravelling of the functions of peroxisomes in metabolism, and it is now well established that peroxisomes are indispensable organelles, especially in higher eukaryotes. Peroxisomes catalyse a number of essential metabolic functions including fatty acid beta-oxidation, ether phospholipid biosynthesis, fatty acid alpha-oxidation and glyoxylate detoxification. The involvement of peroxisomes in these metabolic pathways necessitates the transport of metabolites in and out of peroxisomes. Recently, considerable progress has been made in the characterization of metabolite transport across the peroxisomal membrane. Peroxisomes posses several specialized transport systems to transport metabolites. This is exemplified by the identification of a specific transporter for adenine nucleotides and several half-ABC (ATP-binding cassette) transporters which may be present as hetero- and homo-dimers. The nature of the substrates handled by the different ABC transporters is less clear. In this review we will describe the current state of knowledge of the permeability properties of the peroxisomal membrane. 相似文献
942.
943.
Pugia MJ Jortani SA Basu M Sommer R Kuo HH Murphy S Williamson D Vranish J Boyle PJ Budzinski D Valdes R Basu SC 《Glycoconjugate journal》2007,24(1):5-15
Urinary trypsin inhibitors (uTi) suppress serine proteases during inflammation. After liberation from proinhibitors (P-alpha-I
and I-alpha-I) by the white blood cell (WBC) response, uTi readily pass through the kidneys into urine. A key uTi, bikunin,
is attached to O-linked and N-linked glycoconjugates. Recently, uTi inhibitors, called uristatins, were found to lack the
O-linked glycoconjugates. Monoclonal antibodies were produced using purified uristatin and screened for binding differences
to uristatin, bikunin, P-α-I, and I-α-I. Antibody-binding patterns were characterized using immunoaffinity binding onto protein-chip
surfaces and analysis by Surface Enhanced Laser Desorption/Ionization mass spectrometry (SELDI), using specimens from patients
and from purified uTi standards. Antibodies were developed and used in an enzyme-linked immunosorbent assay (ELISA) method
for uTi measurement in urine and plasma specimens. ELISA was performed on specimens from normal, presumed healthy, controls
and from patients who had been screened for inflammation using a high sensitivity C-reactive protein (CRP) test and a complete
blood count (CBC). Polyclonal antibody against uTi showed cross-reactivity with the Tamm–Horsfall protein (THP) and with proinhibitors.
Screening of anti-uTi monoclonal antibodies (Mab) revealed antibodies that did not cross-react with either of the above, thus
providing a tool to measure both uristatin and bikunin in urine with Mab 3G5 and in plasma with Mab 5D11. The monoclonal antibody
5D11 cross-reacts with specific N-linked glycoconjugates of uristatin present in plasma. In ca 96% of healthy adults, uTi
were present at <12 mg/l in urine and <4 mg/l in plasma. We also found that patients with an inflammation and a CRP of >2.0 mg/l
had higher urinary concentrations of uTi than the control population in every subject. Free uristatin and bikunin pass readily
into urine and are primarily bound to heavy chains that constitute the proinhibitor form in plasma. 相似文献
944.
Base-flipping dynamics in a DNA hairpin processing reaction 总被引:3,自引:2,他引:1
Many enzymes that repair or modify bases in double-stranded DNA gain access to their substrates by base flipping. Although crystal structures provide stunning snap shots, biochemical approaches addressing the dynamics have proven difficult, particularly in complicated multi-step reactions. Here, we use protein–DNA crosslinking and potassium permanganate reactivity to explore the base-flipping step in Tn5 transposition. We present a model to suggest that base flipping is driven by a combination of factors including DNA bending and the intrusion of a probe residue. The forces are postulated to act early in the reaction to create a state of tension, relieved by base flipping after cleavage of the first strand of DNA at the transposon end. Elimination of the probe residue retards the kinetics of nicking and reduces base flipping by 50%. Unexpectedly, the probe residue is even more important during the hairpin resolution step. Overall, base flipping is pivotal to the hairpin processing reaction because it performs two opposite but closely related functions. On one hand it disrupts the double helix, providing the necessary strand separation and steric freedom. While on the other, transposase appears to position the second DNA strand in the active site for cleavage using the flipped base as a handle. 相似文献
945.
The gamma hypothesis states that there are no interactions between antimicrobial environmental factors. The time to growth of Aeromonas hydrophila challenged with pH, NaNO2, and salt combinations at 30°C was investigated. Data were examined using a model based on the gamma hypothesis (the gamma model), which takes into account variance-stabilizing transformations and which gives biologically relevant parameters. At high concentrations of NaNO2 and at pHs of >6.0, the antimicrobial action of the nitrite ion has a strong influence (MIC = 2,033 mg liter−1), whereas at pHs of <6, nitrous acid is dominant (MIC = 1.5 mg liter−1). This change is not due to a “synergy” between pH and the nitrite ion but is due to the shift in the equilibrium concentrations of nitrous acid and nitrite in solution caused by pH. In combination with salt, the parameters found for the action of Na nitrite were identical to those found when it was examined in isolation. Therefore, pH, NaNO2, and salt act independently on the growth of A. hydrophila. By expanding the gamma model with a cardinal temperature model, the results of fitting the model of Palumbo et al. (J. Food Prot. 54:429-435, 1994) to randomly produced environmental conditions could be reproduced, suggesting that temperature also has an independent effect. 相似文献
946.
Formation of Tellurium Nanocrystals during Anaerobic Growth of Bacteria That Use Te Oxyanions as Respiratory Electron Acceptors 总被引:2,自引:1,他引:1 下载免费PDF全文
Shaun M. Baesman Thomas D. Bullen James Dewald Donghui Zhang Seamus Curran Farhana S. Islam Terry J. Beveridge Ronald S. Oremland 《Applied microbiology》2007,73(7):2135-2143
Certain toxic elements support the metabolism of diverse prokaryotes by serving as respiratory electron acceptors for growth. Here, we demonstrate that two anaerobes previously shown to be capable of respiring oxyanions of selenium also achieve growth by reduction of either tellurate [Te(VI)] or tellurite [Te(IV)] to elemental tellurium [Te(0)]. This reduction achieves a sizeable stable-Te-isotopic fractionation (isotopic enrichment factor [] = −0.4 to −1.0 per ml per atomic mass unit) and results in the formation of unique crystalline Te(0) nanoarchitectures as end products. The Te(0) crystals occur internally within but mainly externally from the cells, and each microorganism forms a distinctly different structure. Those formed by Bacillus selenitireducens initially are nanorods (~10-nm diameter by 200-nm length), which cluster together, forming larger (~1,000-nm) rosettes composed of numerous individual shards (~100-nm width by 1,000-nm length). In contrast, Sulfurospirillum barnesii forms extremely small, irregularly shaped nanospheres (diameter < 50 nm) that coalesce into larger composite aggregates. Energy-dispersive X-ray spectroscopy and selected area electron diffraction indicate that both biominerals are composed entirely of Te and are crystalline, while Raman spectroscopy confirms that they are in the elemental state. These Te biominerals have specific spectral signatures (UV-visible light, Raman) that also provide clues to their internal structures. The use of microorganisms to generate Te nanomaterials may be an alternative for bench-scale syntheses. Additionally, they may also generate products with unique properties unattainable by conventional physical/chemical methods. 相似文献
947.
Murata Y Tsuruzoe K Kawashima J Furukawa N Kondo T Motoshima H Igata M Taketa K Sasaki K Kishikawa H Kahn CR Toyonaga T Araki E 《Biochemical and biophysical research communications》2007,364(2):301-307
Insulin receptor substrate-1 (IRS-1) is the major substrate of both the insulin receptor and the IGF-1 receptor. In this study, we created IRS-1 transgenic (IRS-1-Tg) mice which express human IRS-1 cDNA under control of the mouse IRS-1 gene promoter. In the IRS-1-Tg mice, IRS-1 mRNA expression was significantly increased in almost all tissues, but its protein expression was increased in very limited tissues (epididymal fat and skeletal muscle). IRS-1-Tg mice showed glucose intolerance and significantly enlarged epididymal fat mass, as well as elevated serum TNF-α concentrations. Importantly insulin signaling was significantly attenuated in the liver of IRS-1-Tg mice, which may contribute to the glucose intolerance. Our results suggest that excess IRS-1 expression may not provide a beneficial impact on glucose homeostasis in vivo. 相似文献
948.
Michael J. W. Stokesbury Ronan Cosgrove Andre Boustany Daragh Browne Steven L. H. Teo Ronald K. O’Dor Barbara A. Block 《Hydrobiologia》2007,582(1):91-97
Pop-up satellite archival tags were attached to six Atlantic bluefin tuna (Thunnus thynnus) off the west coast of Ireland in autumn 2003 and 2004. The satellite tags measured pressure, ambient temperature and light
for the term of deployment. Radio pop-up satellite endpoint positions, light and sea surface temperature estimations of geolocation
indicate that two fish tagged minutes apart off the coast of County Donegal, migrated to the eastern and western Atlantic
Ocean over the following 8 months. The two fish were 5218 km apart at the termination of the experiment. After tagging in
September and popping up the following March and April, one fish had traveled to the western Atlantic while the other was
located in the waters off the southwest coast of Portugal. A third fish tagged off the coast of County Donegal in October
2004 moved into the Mediterranean Sea and was caught by a fishing vessel southeast of Malta on 11 June 2005. The results link
bluefin tuna feeding on European foraging grounds with known eastern breeding regions and western Atlantic waters. 相似文献
949.
Complexes of Zn(II), Cu(II) and Co(II) with either N-(2-methylpyridyl)-3-thienyl-alkyl-carboxamide or N-(2-pyridyl)-3-thienylalkyl-carboxamide groups have been prepared and characterized. Crystal structures of ten new complexes are reported and discussed. N-(2-Methylpyridyl)-3-thienyl-alkyl-carboxamide exhibits both uni- and bidentate behavior. With all ligands, bidentate complexation is through the carbonyl oxygen and pyridine nitrogen atoms (O, N) and the amide nitrogen atom remains protonated. The electrochemical behavior and the infrared spectra of selected complexes are discussed. 相似文献
950.
Cees S. Roselaar Ronald Sluys Mansour Aliabadian Peter G. M. Mekenkamp 《Journal of Ornithology》2007,148(3):271-280
A database was created of digitized equal area distribution maps of 3,036 phylogenetic species of Palearctic songbirds. Biogeographic
patterns are reported for two data sets: (1) including all passeriform bird species reported as breeding within the boundaries
of our study map, (2) passeriform species restricted in their distribution to our study region, thus excluding the partly
extra-limital taxa. With respect to the data set excluding partly extra-limital taxa, the average range size is 238 grid cells
(grid cell area: 4,062 km2). Analysis of the geographic distribution of species richness for the full data set showed several hotspot regions, mostly
located in mountainous areas. The index of range-size rarity identified similar hotspot regions as that for species richness,
albeit that the range-size rarity de-emphasized the central Siberian hotspot. Range-size rarity hotspots that are not evident
on the measure of species richness concern a great number of islands. Much more prominent on the index of range-size rarity
are the Atlas Mountains of northern Africa, the Jabal al Akhdar region in NE Libya, and the eastern border of the Mediterranean.
Restricting the analysis of geographic variation to the 25% of the species with smallest ranges resulted in a greatly simplified
pattern of hotspots.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献