全文获取类型
收费全文 | 7098篇 |
免费 | 595篇 |
国内免费 | 5篇 |
出版年
2023年 | 25篇 |
2022年 | 67篇 |
2021年 | 106篇 |
2020年 | 75篇 |
2019年 | 87篇 |
2018年 | 113篇 |
2017年 | 131篇 |
2016年 | 173篇 |
2015年 | 302篇 |
2014年 | 409篇 |
2013年 | 456篇 |
2012年 | 586篇 |
2011年 | 529篇 |
2010年 | 346篇 |
2009年 | 293篇 |
2008年 | 364篇 |
2007年 | 397篇 |
2006年 | 372篇 |
2005年 | 355篇 |
2004年 | 323篇 |
2003年 | 323篇 |
2002年 | 303篇 |
2001年 | 82篇 |
2000年 | 85篇 |
1999年 | 82篇 |
1998年 | 83篇 |
1997年 | 68篇 |
1996年 | 68篇 |
1995年 | 56篇 |
1994年 | 62篇 |
1993年 | 52篇 |
1992年 | 91篇 |
1991年 | 57篇 |
1990年 | 63篇 |
1989年 | 57篇 |
1988年 | 46篇 |
1987年 | 41篇 |
1986年 | 36篇 |
1985年 | 40篇 |
1984年 | 53篇 |
1983年 | 39篇 |
1982年 | 34篇 |
1981年 | 39篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 23篇 |
1975年 | 29篇 |
1974年 | 40篇 |
1973年 | 22篇 |
1972年 | 25篇 |
排序方式: 共有7698条查询结果,搜索用时 15 毫秒
1.
E Estébanez-Perpi?á A Bayés J Vendrell M A Jongsma D P Bown J A Gatehouse R Huber W Bode F X Avilés D Reverter 《Journal of molecular biology》2001,313(3):629-638
The cotton bollworm Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) is one of the most serious insect pests in Australia, India and China. The larva causes substantial economical losses to legume, fibre, cereal oilseed and vegetable crops. This pest has proven to be difficult to control by conventional means, mainly due to the development of pesticide resistance. We present here the 2.5 A crystal structure from the novel procarboxypeptidase (PCPAHa) found in the gut extracts from H. armigera larvae, the first one reported for an insect. This metalloprotease is synthesized as a zymogen of 46.6 kDa which, upon in vitro activation with Lys-C endoproteinase, yields a pro-segment of 91 residues and an active carboxypeptidase moiety of 318 residues. Both regions show a three-dimensional structure quite similar to the corresponding structures in mammalian digestive carboxypeptidases, the most relevant structural differences being located in the loops between conserved secondary structure elements, including the primary activation site. This activation site contains the motif (Ala)(5)Lys at the C terminus of the helix connecting the pro- and the carboxypeptidase domains. A remarkable feature of PCPAHa is the occurrence of the same (Ala)(6)Lys near the C terminus of the active enzyme. The presence of Ser255 in PCPAHa instead of Ile and Asp found in the pancreatic A and B forms, respectively, enlarges the S1' specificity pocket and influences the substrate preferences of the enzyme. The C-terminal tail of the leech carboxypeptidase inhibitor has been modelled into the PCPAHa active site to explore the substrate preferences and the enzymatic mechanism of this enzyme. 相似文献
2.
3.
Denise Risch Nicholas J. Gales Jason Gedamke Lars Kindermann Douglas P. Nowacek Andrew J. Read Ursula Siebert Ilse C. Van Opzeeland Sofie M. Van Parijs Ari S. Friedlaender 《Biology letters》2014,10(4)
For decades, the bio-duck sound has been recorded in the Southern Ocean, but the animal producing it has remained a mystery. Heard mainly during austral winter in the Southern Ocean, this ubiquitous sound has been recorded in Antarctic waters and contemporaneously off the Australian west coast. Here, we present conclusive evidence that the bio-duck sound is produced by Antarctic minke whales (Balaenoptera bonaerensis). We analysed data from multi-sensor acoustic recording tags that included intense bio-duck sounds as well as singular downsweeps that have previously been attributed to this species. This finding allows the interpretation of a wealth of long-term acoustic recordings for this previously acoustically concealed species, which will improve our understanding of the distribution, abundance and behaviour of Antarctic minke whales. This is critical information for a species that inhabits a difficult to access sea-ice environment that is changing rapidly in some regions and has been the subject of contentious lethal sampling efforts and ongoing international legal action. 相似文献
4.
5.
Kirsten Skamstrup Hansen Stefan Vieths Helle Vestergaard Per Stahl Skov Carsten Bindslev-Jensen Lars K. Poulsen 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,756(1-2)
The aim of the study was to investigate the possibility of a seasonal variation in reactivity to apples in 27 birch pollen allergic patients. Before and during the birch pollen season 1998, the patients were subjected to double-blind, placebo-controlled food challenges (DBPCFCs) with grated fresh Golden Delicious apple followed by an open food challenge with whole fresh apple. The clinical reactions elicited during the challenges were evaluated both by the patients and the investigators. Moreover, the skin reactivity and the in vitro reactivity to apple were evaluated by skin prick test (SPT), leukocyte histamine release (HR), measurement of specific IgE, and immunoblotting experiments. The sensitivity of the DBPCFC, when compared with the result of the open challenge, was 0.74 (14/19) before the season and 0.80 (16/20) during the season. None of the patients reacted to the blinded challenge without a subsequent reaction to the open challenge. One placebo reaction was registered both before and in season, but not in the same patient. The patient scores of the first positive challenges, and the maximal scores of each combined blinded and open challenge session, were significantly increased during the pollen season (P<0.05). The scores of the open challenge were significantly higher than the scores of the DBPCFC both before the season and during the in-season challenges (P<0.05). Specific IgE against Golden Delicious increased during season (P<0.05), while neither SPT, HR, nor immunoblotting experiments could confirm an increase in reactivity. In conclusion, the results of the oral challenge tests indicated an increase in clinical reactivity to apples during the birch pollen season in birch pollen allergic individuals. 相似文献
6.
7.
8.
Riccardo E. Marioni Lars Penke Gail Davies Jennifer E. Huffman Caroline Hayward Ian J. Deary 《Proceedings. Biological sciences / The Royal Society》2014,281(1781)
Human cognitive ability shows consistent, positive associations with fitness components across the life-course. Underlying genetic variation should therefore be depleted by selection, which is not observed. Genetic variation in general cognitive ability (intelligence) could be maintained by a mutation–selection balance, with rare variants contributing to its genetic architecture. This study examines the association between the total number of rare stop-gain/loss, splice and missense exonic variants and cognitive ability in childhood and old age in the same individuals. Exome array data were obtained in the Lothian Birth Cohorts of 1921 and 1936 (combined N = 1596). General cognitive ability was assessed at age 11 years and in late life (79 and 70 years, respectively) and was modelled against the total number of stop-gain/loss, splice, and missense exonic variants, with minor allele frequency less than or equal to 0.01, using linear regression adjusted for age and sex. In both cohorts and in both the childhood and late-life models, there were no significant associations between rare variant burden in the exome and cognitive ability that survived correction for multiple testing. Contrary to our a priori hypothesis, we observed no evidence for an association between the total number of rare exonic variants and either childhood cognitive ability or late-life cognitive ability. 相似文献
9.
Lars Terenius Björn Johansson 《Biochemical and biophysical research communications》2010,396(1):140-142
This mini-review outlines the opioid systems and their roles primarily as related to reward and compulsive drug/alcohol intake. The central role is taken by the mu-opioid receptor, target for opiate analgesics and also a central target in compulsive alcohol abuse, alcoholism. The mu-opioid receptor and the cognate opioid neuropeptides from proenkephalin and proopiomelancortin are members of a superfamily of opioid systems, each with unique and still to be defined roles in the central nervous system. 相似文献
10.
The occurrence of bikunin and ·1-microglobuli n was investigated in human ovary and Fallopian tubes. Bikunin and ·1-microglobulin are transcribed in the liver from a common gene. Bikunin immunoreactivity was detected in the zona pellucida.
A positive reaction for bikunin was also observed in connective tissue of the oviduct. In addition, mast cells showed a more
intense posi tive reaction than the surrounding connective tissue. Specific displaceable ·1-microglobulin immunoreactivity was revealed in the zona pellucida. The data suggest that bikunin and ·1- microglobulin are trapped in the zona pellucida.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献