全文获取类型
收费全文 | 5092篇 |
免费 | 214篇 |
国内免费 | 13篇 |
专业分类
5319篇 |
出版年
2023年 | 54篇 |
2022年 | 142篇 |
2021年 | 297篇 |
2020年 | 126篇 |
2019年 | 171篇 |
2018年 | 189篇 |
2017年 | 148篇 |
2016年 | 217篇 |
2015年 | 256篇 |
2014年 | 287篇 |
2013年 | 413篇 |
2012年 | 364篇 |
2011年 | 369篇 |
2010年 | 206篇 |
2009年 | 176篇 |
2008年 | 197篇 |
2007年 | 192篇 |
2006年 | 176篇 |
2005年 | 148篇 |
2004年 | 118篇 |
2003年 | 89篇 |
2002年 | 94篇 |
2001年 | 57篇 |
2000年 | 62篇 |
1999年 | 48篇 |
1998年 | 29篇 |
1997年 | 15篇 |
1996年 | 21篇 |
1995年 | 17篇 |
1993年 | 18篇 |
1992年 | 34篇 |
1991年 | 47篇 |
1990年 | 41篇 |
1989年 | 33篇 |
1988年 | 28篇 |
1987年 | 42篇 |
1986年 | 31篇 |
1985年 | 36篇 |
1984年 | 28篇 |
1983年 | 20篇 |
1982年 | 17篇 |
1980年 | 13篇 |
1979年 | 23篇 |
1978年 | 26篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 15篇 |
1974年 | 15篇 |
1973年 | 23篇 |
1970年 | 13篇 |
排序方式: 共有5319条查询结果,搜索用时 15 毫秒
71.
The complete cDNA sequences of two clones encoding beta-tubulin isotypes and the partial sequence of a third isoform from Chinese hamster ovary cells have been determined. The deduced amino acid sequences of the three isoforms show extensive homology to each other as well as with other alpha and beta-tubulin sequences from various species. These results provide evidence for the expression of three different isoforms of beta-tubulin in Chinese hamster ovary cells. 相似文献
72.
Mammalian pyruvate carboxylase: effect of biotin on the synthesis and translocation of apo-enzyme into 3T3-L adipocyte mitochondria 总被引:1,自引:0,他引:1
The effect of biotin on the induction (and possible requirement for uptake into mitochondria) of apopyruvate carboxylase has been examined in 3T3-L adipocytes. Cells fed biotin-sufficient medium contained only holoenzyme in mitochondria and no apoenzyme was detected. The amount of apoenzyme elaborated in biotin-deficient 3T3-L adipocytes was comparable to the holopyruvate carboxylase protein found in cells maintained on biotin-sufficient medium. Like the holoenzyme, the apoenzyme was detected exclusively in the mitochondrial fraction of 3T3-L adipocytes. This indicates that the synthesis of apopyruvate carboxylase and its translocation into mitochondria occur independently of the cofactor, biotin. 相似文献
73.
S. Ahmad P. K. Roy A. W. Khan S. K. Basu B. N. Johri 《World journal of microbiology & biotechnology》1991,7(5):557-561
A wild-type strain of Rhodococcus equi, isolated from soil, degraded cholesterol, -sitosterol, stigmasterol and mixed sterois to androst-4-ene-3,17-dione (AD) and androsta-1,4-diene-3,17-dione (ADD). A definite preference for a relatively simply structured cholesterol side chain was observed. Highest specific cholesterol side-chain cleavage was associated with active growth of the culture. Maximum yield of ADD was obtained when sodium acetate and cholesterol were incorporated together in the medium. Specific side-chain cleavage required the presence of 2,2-dipyridyl, an inhibitor of ring cleavage.S. Ahmad and B.N. Johri are with the Department of Microbiology, College of Basic Sciences and Humanities, G.B. Pant University of Agriculture and Technology, Pantriagar 263 145, Nainital, UP, India. P.K. Roy, A.W. Khan and S.K. Basu are at Fermentation Technology Division, Central Drug Research Institute, Lucknow, India. 相似文献
74.
The ultrastructural indicators of aquatic ecosystem health 总被引:4,自引:0,他引:4
Gary G. Leppard Mohiuddin Munawar 《Journal of Aquatic Ecosystem Stress and Recovery (Formerly Journal of Aquatic Ecosystem Health)》1992,1(4):309-317
Analyses by transmission electron microscopy (TEM) of the smallest organisms in surface waters can be used to assess ecosystem health; the evidence for this statement is reviewed and recommendations are made for optimal use of TEM technology in providing such assessments. Those groups of small organisms currently being considered as indicators of ecosystem health (viruses, bacteria, autotrophic picoplankton, and autotrophic nanoplankton) are reviewed briefly as subjects for monitoring by TEM. New information on direct counting by TEM of viral femtoplankton indicates that viruses can be present in numbers 103 to 107 times greater than previously estimated by the traditional counts of plaque-forming units using various host bacteria. Such concentrations indicate that virus infections may exert ecological control over planktonic microbes. Ultrastructural research on prokaryotic picoplankton suggests that TEM analyses of cells in ultra-thin sections can be used to speciate the picoplankton and to diagnose them for cytological modifications related to environmental stress. Considering their great importance, episodically, to primary productivity and to modulating the speciation of higher levels in the food web, such picoplankton ultrastructural analyses could be pursued with profit as a diagnostic tool. For decades, the ultrastructure of some eukaryotic nanoplankton has been known to vary in specific ways to specific stresses in laboratory experiments. An extension of these structure-function correlations is potentially a useful tool to provide indicators of ecosystem health. The barriers to progress in such research are now understood and can be overcome. 相似文献
75.
Sanjay Awasthi Faiyaz Ahmad
Rashmi Sharma
Hassan Ahmad 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1992,584(2):167-173A chromatographic method for the specific determination of glutathione in malignant cell lines is described. The method is based on the ability of glutathione-S-transferase to specifically and quantitatively conjugate glutathione to 1-chloro-2,4-dinitrobenzene and chromatographic quantitation of the resultant conjugate, dinitrophenyl-S-glutathione, by reversed-phase liquid chromatography. The assay can be performed on 20 000 g supernatants of cell homogenates without acid extraction. 2-Mercaptoethanol, a sulfhydryl compound often used as a thiol-protective agent to preserve enzymatic activities of a number of enzymes, did not interfere with glutathione determination by this method. The dinitrophenyl-S-glutathione isolated from either standard glutathione samples or from cell homogenates was shown to be identical to authentic dinitrophenyl-S-glutathione using mass spectrometry. Recovery of glutathione in standard samples by the current method was identical to that determined using 5,5′-dithiobis(2-nitrobenzoic acid). Exogenous glutathione added to supernatants of cell homogenate in the presence or absence of 2-mercaptoethanol was also completely recovered. 相似文献
76.
Rapid expulsion of Trichinella spiralis could be transferred to naive adult rats with thoracic duct lymphocytes and immune serum. Thoracic duct cells collected from Days 3-5 and immune serum collected on Day 28, respectively, after infection were effective. Both cells and serum were unable to transfer rapid expulsion when given alone, even in large volumes. Recipients of immune serum and cells eliminated a significantly higher number of larvae than control rats by 1 hr after challenge with muscle larvae. Rapid expulsion produced 30-80% larval worm rejection but could not be increased by the transfer of more cells or immune serum. Mucus trappings did not appear to play a role in the rejection process. After transfer of 2 x 10(8) cells and 4.0 ml immune serum, rapid expulsion persisted for less than 1 week. However, after adoptive transfer of cells alone, the gut remained functionally receptive to the passive transfer of immune serum for 7 weeks. Therefore, the changes effected by transfer of cells were long lived in contrast to the 1 week, or less, of functional persistence by transferred immune serum. The data indicate that two separate processes, one cell mediated and the other immune serum mediated, interact synergistically in the intestine and lead to the expression of rapid expulsion. 相似文献
77.
M Alam M Ahmad A Rasheed M Saleem M K Javaid S Ikram 《Indian journal of experimental biology》1990,28(10):940-942
The metabolic fate of isatin hydrazone (Ia), isatin-3-thiosemicarbazone (Ib), isatin-3-semicarbazone (Ic), isatin-3-phenylhydrazone (Id), isatin oxime (Ie) and 3-hydroxy-3-acetonyl oxindole (II) was studied in rabbits. The compounds were administered orally in the dose of 300 mg/kg body wt. Isatin anthranilic acid, tryptophan and nicotinic acid were identified as the major metabolites excreted in urine. The 3-hydroxy-3-acetonyl oxindole (II) gave on additional metabolite, oxindole. The major metabolites were separated and identified unambiguously on thin layer silica gel plate. Metabolic pathways have been proposed to explain the biotransformation of the compounds investigated. 相似文献
78.
Three enzymes involved in the conversion of 3T3-L2 fibroblasts into fat cells, acetyl CoA carboxylase (ACC), fatty acid synthetase (FAS) and pyruvate carboxylase (PC) have been localized by immunofluorescence techniques. The method enables the identification of cells undergoing the conversion while they are still fibroblastic in appearance, often before the obvious appearance of fat droplets. Specific fluorescence for each enzyme can be seen in "clones" of cells derived from single cells, which may undergo an event during logarithmic growth, which programs the cells to differentiate subsequent to confluence of and addition of induction medium. 相似文献
79.
80.