全文获取类型
收费全文 | 9314篇 |
免费 | 823篇 |
国内免费 | 1244篇 |
出版年
2024年 | 15篇 |
2023年 | 125篇 |
2022年 | 278篇 |
2021年 | 448篇 |
2020年 | 334篇 |
2019年 | 468篇 |
2018年 | 391篇 |
2017年 | 294篇 |
2016年 | 396篇 |
2015年 | 578篇 |
2014年 | 705篇 |
2013年 | 720篇 |
2012年 | 908篇 |
2011年 | 923篇 |
2010年 | 551篇 |
2009年 | 459篇 |
2008年 | 535篇 |
2007年 | 491篇 |
2006年 | 456篇 |
2005年 | 347篇 |
2004年 | 309篇 |
2003年 | 284篇 |
2002年 | 237篇 |
2001年 | 174篇 |
2000年 | 131篇 |
1999年 | 128篇 |
1998年 | 103篇 |
1997年 | 88篇 |
1996年 | 81篇 |
1995年 | 45篇 |
1994年 | 67篇 |
1993年 | 33篇 |
1992年 | 47篇 |
1991年 | 33篇 |
1990年 | 23篇 |
1989年 | 18篇 |
1988年 | 17篇 |
1987年 | 26篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 5篇 |
1980年 | 7篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 8篇 |
1971年 | 9篇 |
1970年 | 4篇 |
1967年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 585 毫秒
71.
本文通过对枯草芽孢杆菌BR151衍生株与北京棒杆菌1134衍生株的赖氨酸高产融合子Q4413株的形态学、生理生化特性等方面的研究,揭示了融合子与双亲株在这些方面的差异,为Q4413株确系双亲株的重组子或新的融合子增加了佐证. 相似文献
72.
73.
Location of a Bombyx mori receptor binding region on a Bacillus thuringiensis delta-endotoxin. 总被引:7,自引:0,他引:7
Receptor binding studies were performed with 125I-labeled trypsin-activated insecticidal toxins, CryIA(a) and CryIA(c), from Bacillus thuringiensis on brush-border membrane vesicles (BBMV) prepared from Bombyx mori larval midgut. Bioassays were performed by gently force feeding B. mori with diluted toxins. CryIA(a) toxin (LD50; 0.002 micrograms) was 200 times more active against B. mori larvae than CryIA(c) toxin (LD50; 0.421 micrograms) and showed high-affinity saturable binding. The Kd and the binding site concentration for CryIA(a) toxin were 3.5 nM and 7.95 pmol/mg, respectively. CryIA(c) toxin (Kd, 50.35 nM; Bmax, 2.85 pmol/mg) did not demonstrate high-affinity binding to B. mori BBMV. Control experiments with CryIA(a) and CryIA(c) toxins revealed no binding to mouse small intestine BBMV and nonspecific binding to pig kidney BBMV. These data provide evidence that binding to a specific receptor on the membrane of midgut epithelial cells is an important determinant with respect to differences in insecticidal spectrum of insecticidal crystal proteins. To locate a B. mori receptor binding region on the CryIA(a) toxin, homologous and heterologous competition binding studies were performed with a set of mutant proteins which had previously been used to define the B. mori "specificity domain" on this toxin (Ge, A. Z., Shivarova, N. I., and Dean, D. H. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 4037-4041). These mutant proteins have had regions of their genes reciprocally exchanged with the cryIA(c) gene. A B. mori receptor binding region on CryIA(a) toxin includes the amino-terminal portion of the hypervariable region, amino acids 332-450, which is identical to the previously described B. mori specificity determining region. These data provide direct evidence that delta-endotoxins contain a tract of amino acids that comprise a binding region and as a results determines the specificity of a toxin. 相似文献
74.
A new simplified procedure for determination of nitric oxide (NO) in biological solutions is described utilizing a new reducing system of nitric oxide prior to chemiluminescence. Advantages of the new method makes heating of the reducing solution unnecessary and avoids cooling and condensation of generated vapors. Only traces of acid with a high boiling point are used. The method permits analysis of small sample volumes (200 microL). The basal production of nitric oxide by freshly harvested endothelial cells ranged from 100 to 880 picomoles. 相似文献
75.
A hybrid cell mapping panel for regional localization of probes to human chromosome 8 总被引:6,自引:0,他引:6
We have characterized a panel of somatic cell hybrids that carry fragments of human chromosome 8 and used this panel for the regional localization of anonymous clones derived from a chromosome 8 library. The hybrid panel includes 11 cell lines, which were characterized by Southern blot hybridization with chromosome 8-specific probes of known map location and by fluorescent in situ hybridization with a probe derived from a chromosome 8 library. The chromosome fragments in the hybrid cell lines divide the chromosome into 10 intervals. Using this mapping panel, we have mapped 56 newly derived anonymous clones to regions of chromosome 8. We have also obtained physical map locations for 7 loci from the genetic map of chromosome 8, thus aligning the genetic and physical maps of the chromosome. 相似文献
76.
The entomopathogenic fungus,Beauveria bassiana (Balsamo) Vuillemin, was applied to whorl-stage (V7) corn,Zea mays L., by foliar application of a granular formulation of corn grits containing conidia or by injection of a conidial suspension.
All plants were infested with European corn borer larvae,Ostrinia nubilalis (Hübner), at the V7 (whorl), V12 (late-whorl), or V17 (pretassel) stage of plant development. Plants infested at whorl and
late-whorl stages had significantly more European corn borer tunneling than did plants infested at the pretassel stage. The
percentage of plants colonized byB. bassiana did not differ significantly among the whorl, late-whorl, and pretassel stages. As the plants matured,B. bassiana was isolated from different plant areas, with the pith more frequently colonized than the leaf collars. Foliar application
ofB. bassiana provided immediate suppression ofO. nubilalis in those plants infested at whorl stage. The reduced efficacy ofB. bassiana at the intermediate plant stages relative to efficacy at harvest is discussed.
The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of
Agriculture over other firms or similar products not mentioned. 相似文献
77.
本文用~(125)Ⅰ标记LC-1进行了一些体内外实验。实验结果表明:LC-1单抗的结合常数为4.8×10~8M~(-1),LC-1针对的SPC-A_1细胞表面抗原的位点数为7.2×10~4/细胞;LC-1与LAC-122两单抗针对的抗原决定簇没有交叉;用蛋白酶和过碘酸钠处理SPC-A_1细胞,前者对LC-1的结合抑制39%,后者抑制66%;LC- 1不但有较强的体外结合靶细胞的能力,从LC-1在荷瘤裸鼠中的组织器官分布来看,LC-1与肿瘤有较高的体内亲和性,并且是特异性的结合。 相似文献
78.
Epidemic hemorrhagic fever in Hubei Province, The People's Republic of China: a clinical and serological study 总被引:1,自引:0,他引:1
M S Cohen J Casals G D Hsiung H E Kwei C C Chin H C Ge C M Hsiang P W Lee C J Gibbs D C Gajdusek 《The Yale journal of biology and medicine》1981,54(1):41-55
Between July 1975 and April 1980, 71 patients were admitted to the Second Attached Hospital of Hubei Provincial Medical College in Wuchang with the diagnosis of epidemic hemorrhagic fever (EHF). The clinical course among these patients was similar to that described for patients with Korean hemorrhagic fever, and hemorrhagic fever with renal syndrome of the U.S.S.R. The overall mortality was 11.2 percent. Sera obtained from some of these patients as well as from patients admitted to the First Attached Hospital of Hubei Provincial Medical College were tested against an antigen associated with Korean hemorrhagic fever and showed exceedingly high antibody titers. We conclude that EHF in Central China represents the same or a closely related disease process as Korean hemorrhagic fever. 相似文献
79.
J S Sarma R Fischer S Ikeda R J Bing 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1976,151(2):303-306
The iv injection of 7-ketocholesterol into rabbits, made soluble by combining with bile salts, inhibited cholesterol uptake by the aorta. However, the inhibition was not as marked or as uniform as previously demonstrated in in vitro experiments. This difference may have been the result of lower plasma concentrations of 7-ketocholesterol in the injected animals. Gastric feeding of 7-ketocholesterol failed to inhibit aortic cholesterol uptake, probably because of inadequate plasma concentrations of the inhibitory steroid. The results suggest that the mechanism of 7-ketocholesterol on aortic cholesterol uptake is through competitive inhibition. 相似文献
80.
Establishment of axon and dendrite polarity, migration to a desired location in the developing brain, and establishment of proper synaptic connections are essential processes during neuronal development. The cellular and molecular mechanisms that govern these processes are under intensive investigation. The function of the centrosome in neuronal development has been examined and discussed in few recent studies that underscore the fundamental role of the centrosome in brain development. Clusters of emerging studies have shown that centrosome positioning tightly regulates neuronal development, leading to the segregation of cell factors, directed neurite differentiation, neuronal migration, and synaptic integration. Furthermore, cilia, that arise from the axoneme, a modified centriole, are emerging as new regulatory modules in neuronal development in conjunction with the centrosome. In this review, we focus on summarizing and discussing recent studies on centrosome positioning during neuronal development and also highlight recent findings on the role of cilia in brain development. We further discuss shared molecular signaling pathways that might regulate both centrosome and cilia associated signaling in neuronal development. Furthermore, molecular determinants such as DISC1 and LKB1 have been recently demonstrated to be crucial regulators of various aspects of neuronal development. Strikingly, these determinants might exert their function, at least in part, via the regulation of centrosome and cilia associated signaling and serve as a link between these two signaling centers. We thus include an overview of these molecular determinants. 相似文献