全文获取类型
收费全文 | 264405篇 |
免费 | 24208篇 |
国内免费 | 254篇 |
出版年
2018年 | 3034篇 |
2017年 | 2981篇 |
2016年 | 3877篇 |
2015年 | 4086篇 |
2014年 | 5080篇 |
2013年 | 7354篇 |
2012年 | 8616篇 |
2011年 | 9388篇 |
2010年 | 6182篇 |
2009年 | 5343篇 |
2008年 | 8129篇 |
2007年 | 8325篇 |
2006年 | 7906篇 |
2005年 | 7446篇 |
2004年 | 7292篇 |
2003年 | 7089篇 |
2002年 | 6919篇 |
2001年 | 12688篇 |
2000年 | 12768篇 |
1999年 | 9508篇 |
1998年 | 2862篇 |
1997年 | 2884篇 |
1996年 | 2856篇 |
1995年 | 2627篇 |
1994年 | 2555篇 |
1993年 | 2452篇 |
1992年 | 7301篇 |
1991年 | 7104篇 |
1990年 | 7191篇 |
1989年 | 6969篇 |
1988年 | 6475篇 |
1987年 | 6119篇 |
1986年 | 5463篇 |
1985年 | 5804篇 |
1984年 | 4611篇 |
1983年 | 3986篇 |
1982年 | 2830篇 |
1981年 | 2639篇 |
1980年 | 2407篇 |
1979年 | 4224篇 |
1978年 | 3225篇 |
1977年 | 2968篇 |
1976年 | 2902篇 |
1975年 | 3349篇 |
1974年 | 3581篇 |
1973年 | 3593篇 |
1972年 | 3104篇 |
1971年 | 2903篇 |
1970年 | 2570篇 |
1969年 | 2356篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
S A Bitko L O Dynga A R Shikhman Z F Shmakova N I Briko 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1990,(4):3-7
The amino acid composition of cell walls and surface proteins, isolated from virulent (M+) and avirulent (M-) streptococcal strains (group A, type 29) has been determined by the method of E. H. Beachey et al. The kinetics of the lysis and proteolysis of streptococcal cell walls with muramidase and protease obtained from Actinomyces levoris and streptolysin has been studied. The constants describing the progress rates of these processes has been determined; their values in case of both lysis and proteolysis are higher in virulent strains than in avirulent ones. 相似文献
962.
Construction of isogenic gonococci with variable porin structure: effects on susceptibility to human serum and antibiotics 总被引:11,自引:2,他引:9
Protein I (PI) is the most abundant protein on the gonococcal cell surface and besides its porin function it may have important properties contributing to pathogenicity. By allelic exchange using cloned PI genes from FA19 (PIA) and MS11 (PIB) and a selectable marker introduced closely downstream of these genes, we constructed sets of isogenic gonococcal strains that differ only in their PI gene. Analysis revealed that PI has a major effect on stable resistance to normal human serum, and a slight effect on low-level resistance to antibiotics. All PIA/B hybrids were hypersusceptible to serum, suggesting a possible explanation for why such hybrids do not occur in nature. 相似文献
963.
964.
Scalp reconstruction with a prefabricated abdominal flap carried by the radial artery. 总被引:3,自引:0,他引:3
Custom prefabrication of free flaps provides an unlimited variety of applications, since flaps can be created with expendable tissues and without restriction to naturally occurring vascular territories. These principles also can be used to customize flaps that could not be completed by conventional means. We report a case of scalp reconstruction using a random-pattern abdominal flap in which a radial artery fascial flap was induced to serve as the vascular carrier. In addition to providing durable scalp coverage, the prefabricated free flap enabled salvage of an abdominal flap that would otherwise have been aborted after intermediate transfer to the forearm. 相似文献
965.
966.
967.
Journal of Ichthyology - The paper considers the effect of the Sea of Azov salinization on the food supply to anchovy Engraulis encrasicolus maeoticus as the level of salinity was rising from 12.7... 相似文献
968.
Chung-Te Chang Natalia Bercovich Belinda Loh Stefanie Jonas Elisa Izaurralde 《Nucleic acids research》2014,42(8):5217-5233
The removal of the 5′-cap structure by the decapping enzyme DCP2 and its coactivator DCP1 shuts down translation and exposes the mRNA to 5′-to-3′ exonucleolytic degradation by XRN1. Although yeast DCP1 and DCP2 directly interact, an additional factor, EDC4, promotes DCP1–DCP2 association in metazoan. Here, we elucidate how the human proteins interact to assemble an active decapping complex and how decapped mRNAs are handed over to XRN1. We show that EDC4 serves as a scaffold for complex assembly, providing binding sites for DCP1, DCP2 and XRN1. DCP2 and XRN1 bind simultaneously to the EDC4 C-terminal domain through short linear motifs (SLiMs). Additionally, DCP1 and DCP2 form direct but weak interactions that are facilitated by EDC4. Mutational and functional studies indicate that the docking of DCP1 and DCP2 on the EDC4 scaffold is a critical step for mRNA decapping in vivo. They also revealed a crucial role for a conserved asparagine–arginine containing loop (the NR-loop) in the DCP1 EVH1 domain in DCP2 activation. Our data indicate that DCP2 activation by DCP1 occurs preferentially on the EDC4 scaffold, which may serve to couple DCP2 activation by DCP1 with 5′-to-3′ mRNA degradation by XRN1 in human cells. 相似文献
969.
Relationships between the strongyloid nematodesRugopharynx delta, R. zeta, R. omega, R. longibursaris, R. mawsonae andR. sigma, all from macropodid marsupials, were investigated using allozyme data. The phylogenetic trees derived from the electrophoretic data set were congruent with those of the hosts and were consistent with the hypothesis that the species complex originated in pademelons of the genusThylogale and diversified in rock-wallabies (Petrogale spp.) and scrub wallabies of the subgenusNotamacropus. Host switching is evident only between closely related macropodid taxa. 相似文献
970.
John A. Nyakatura Vivian R. Allen Jonas Laustr?er Amir Andikfar Marek Danczak Hans-Jürgen Ullrich Werner Hufenbach Thomas Martens Martin S. Fischer 《PloS one》2015,10(9)
Orobates pabsti, a basal diadectid from the lower Permian, is a key fossil for the understanding of early amniote evolution. Quantitative analysis of anatomical information suffers from fragmentation of fossil bones, plastic deformation due to diagenetic processes and fragile preservation within surrounding rock matrix, preventing further biomechanical investigation. Here we describe the steps taken to digitally reconstruct MNG 10181, the holotype specimen of Orobates pabsti, and subsequently use the digital reconstruction to assess body mass, position of the centre of mass in individual segments as well as the whole animal, and study joint mobility in the shoulder and hip joints. The shape of most fossil bone fragments could be recovered from micro-focus computed tomography scans. This also revealed structures that were hitherto hidden within the rock matrix. However, parts of the axial skeleton had to be modelled using relevant isolated bones from the same locality as templates. Based on the digital fossil, mass of MNG 10181 was estimated using a model of body shape that was varied within a plausible range to account for uncertainties of the dimension. In the mean estimate model the specimen had an estimated mass of circa 4 kg. Varying of the mass distribution amongst body segments further revealed that Orobates carried most of its weight on the hind limbs. Mostly unrestricted joint morphology further suggested that MNG 10181 was able to effectively generate propulsion with the pelvic limbs. The digital reconstruction is made available for future biomechanical studies. 相似文献