全文获取类型
收费全文 | 11608篇 |
免费 | 1053篇 |
国内免费 | 6篇 |
出版年
2022年 | 68篇 |
2021年 | 143篇 |
2020年 | 95篇 |
2019年 | 97篇 |
2018年 | 152篇 |
2017年 | 134篇 |
2016年 | 227篇 |
2015年 | 362篇 |
2014年 | 368篇 |
2013年 | 561篇 |
2012年 | 663篇 |
2011年 | 699篇 |
2010年 | 401篇 |
2009年 | 408篇 |
2008年 | 600篇 |
2007年 | 590篇 |
2006年 | 569篇 |
2005年 | 552篇 |
2004年 | 533篇 |
2003年 | 563篇 |
2002年 | 549篇 |
2001年 | 140篇 |
2000年 | 109篇 |
1999年 | 124篇 |
1998年 | 149篇 |
1997年 | 100篇 |
1996年 | 112篇 |
1995年 | 103篇 |
1994年 | 97篇 |
1993年 | 91篇 |
1992年 | 92篇 |
1991年 | 83篇 |
1990年 | 88篇 |
1989年 | 88篇 |
1988年 | 74篇 |
1987年 | 83篇 |
1986年 | 62篇 |
1985年 | 82篇 |
1984年 | 90篇 |
1983年 | 96篇 |
1982年 | 102篇 |
1981年 | 103篇 |
1980年 | 96篇 |
1979年 | 75篇 |
1978年 | 76篇 |
1977年 | 88篇 |
1976年 | 96篇 |
1975年 | 71篇 |
1974年 | 76篇 |
1973年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
William J. Matthews Mary E. Power Arthur J. Stewart 《Environmental Biology of Fishes》1986,17(4):291-297
Synopsis
Campostoma spp., widespread and abundant herbivorous minnows of eastern North America, produce distinctive grazing scars when feeding on algae attached to natural substrates in streams. These scars are particularly prominent upon the low growth forms of blue-green algae that dominate the attached algal flora of many upland streams. In one stream pool in the Ozark uplands of Oklahoma, numbers and sizes of grazing scars coincided with numbers and sizes of individual Campostoma that occurred across a depth gradient, demonstrating that the information contained in the scars can provide quantification of microhabitat use and grazing intensity of these important herbivores. The results also support the hypothesis that in environments free of aquatic predators, larger fish use deeper parts of available stream habitats, particularly if threats from terrestrial or avian predators exist. 相似文献
102.
Laurence S. Kaminsky F.Peter Guengerich Ghazi A. Dannan Steven D. Aust 《Archives of biochemistry and biophysics》1983,225(1):398-404
R- and S-warfarin metabolite profiles (regio- and stereoselectivity) have been determined with hepatic microsomes from untreated rats and rats treated with nine individual polybrominated biphenyl (PBB) congeners, a commercial mixture of PBBs, and, for comparison with phenobarbital and 3-methylcholanthrene. The metabolic rates have been correlated with cytochrome P-450 (P-450) isozyme concentrations in the microsomes determined by immunochemical quantitation techniques (G. A. Dannan, F. P. Guengerich, L. S. Kaminsky, and S. D. Aust, (1983) J. Biol. Chem., 258, 1282–1288). The warfarin hydroxylase activities of the P-450 isozyme components of the various microsomal preparations (F. P. Guengerich, G. A. Dannan, S. T. Wright, M. V. Martin, and L. S. Kaminsky (1982) Biochemistry, 21, 6019–6030) were multiplied by the corresponding isozyme concentrations to obtain an assessment of the potential warfarin hydroxylase capacity of the microsomes, and the results were compared with actual activities. The results of these studies and comparisons indicate that substrate regio- and stereoselectivities of microsomal-bound P-450s are essentially retained on purification of the isozymes to homogeneity and reconstitution, that warfarin metabolism by microsomal preparations can be used to predict microsomal P-450 isozyme compositions, and that microsomal warfarin hydroxylase activity is greater than would be predicted based on the approx 20:1 ratio of P-450 to NADPH-P-450 reductase in the microsomes and on the known activities of constituent isozymes. Two P-450 isozymes which are induced by treatment of rats with phenobarbital appear to be more tightly linked to NADPH-P-450 reductase than does an isozyme induced by β-naphthoflavone. 相似文献
103.
To further understand the mechanism of action by which ethanol (ETOH) decreases plasma luteinizing hormone (LH) levels, the effects of multiple i.p. injections of EOH (1.0--1.5 g/kg) or saline on hypothalamic luteinizing hormone releasing hormone (LHRH) and plasma LH concentrations were evaluated in intact and castrate male rats. After injections, animals were decapitated, brains rapidly removed, and blocks containing the hypothalamus [with median eminence (ME)] were isolated. Hypothalami were subjected to acetic acid extraction and LHRH content quantitated via radioimmunoassay (RIA). Hypothalamic LHRH was found to be inversely correlated with plasma LH. In response to castration, both saline and ETOH-treated rats showed a decrease in hypothalamic LHRH content with a concomitant increase in plasma LH; however, the ETOH-treated animals retained significantly greater concentrations of LHRH and showed significantly lower plasma LH levels when compared to saline-treated controls. Likewise, ETOH-treated intact animals showed significant increases in LHRH content, with LH levels remaining significantly lower than the saline-treated intact controls. Thus, these data from both intact and castrate rats provide evidence to support the hypothesis that alcohol-induced decreases in LH levels are due to a diminished release rate of hypothalamic LHRH. 相似文献
104.
A previous investigation of the structure of the extracellular polysaccharide gum from the nitrogen-fixing Rhizobium strain cb744 (a member of the slow-growing Cowpea group) indicated that there were two β-(1→4)-linked d-glucopyranosyl residues for each α-(1→4)-linked d-mannopyranosyl residue, and that each mannose was substituted at O-6 by a β-d-galactopyranosyl residue having 71% of the galactose present as 4-O-methylgalactose. The present study shows that, although the gum appeared to have a simple tetrasaccharide repeating unit, it is composed of two closely associated components. One is a (1→4)-linked α-d-mannan substituted at each O-6 by a β-d-galactopyranosyl residue (71% 4-O-methylated). The second component is a (1→4)-linked β-d-glucan. The existence of the two polysaccharides was established by separation of the β-d-galactosidase-treated gum on a column of concanavalin A-Sepharose 4B. The d configurations were determined and the anomeric attribution of the linkages confirmed by the use of enzymes. The interaction between the two gum components is discussed. 相似文献
105.
Glucocorticoids Increase Catecholamine Synthesis and Storage in PC 12 Pheochromocytoma Cell Cultures 总被引:10,自引:4,他引:6
Arthur S. Tischler Robert L. Perlman† Gardiner M. Morse Beth E. Sheard† 《Journal of neurochemistry》1983,40(2):364-370
Abstract: Glucocorticoids, cholera toxin and high plating density all increase the activity of tyrosine 3-monooxygenase (TH) in cultured PC12 pheochromocytoma cells. Glucocorticoids increase enzyme activity in cells treated with cholera toxin and in cells grown at high plating density. Glucocorticoids also increase the content of stored catecholamines in the cells. In cells cultured under routine conditions, glucocorticoids primarily increase the stores of dopamine. The addition of ascorbate to the culture medium increases the storage of norepinephrine in both steroid-treated and untreated cells. Incubation of the cells in media containing 56 n M K+ causes the release of the same percentage of stored dopamine from steroid-treated as from untreated cells. Steroid-treated cells contain more dopamine than do untreated cells and therefore, in response to high K+ , the steroid-treated cells secrete more dopamine than do untreated cells. We conclude that the activity of tyrosine 3-monooxygenase in PC12 cells can be regulated by several distinct mechanisms; that glucocorticoids cause a coordinate increase in TH activity and in catecholamine storage; that steroids increase the storage of catecholamines in a releasable pool; and that the steroid-induced increase in catecholamine storage may result in increased secretion of catecholamines from steroid-treated cells. 相似文献
106.
Venkataraman Amarnath Traci L. Miller Arthur D. Broom 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,741(2):224-229
Poly(5-fluoro-2′-deoxyuridylic acid) was synthesized and its properties were compared with those of poly(dT) and poly(dU). It readily complexed with poly(dA). The 1:1 complex melted at about 20°C lower than poly(dA) · poly(dT). A triple-stranded helix, poly(dA)·2 poly(dF5U) was formed only in high salt (2.0 M NaCl). 相似文献
107.
108.
Arthur E. Greene Jesse Charney Warren W. Nichols Lewis L. Coriell 《In vitro cellular & developmental biology. Plant》1972,7(6):313-322
Summary Three mosquito cell cultures designated as Suitor's clone ofAedes aegypti, Culiseta inornata andAedes vexans were shown to be moth by immunological, karyological, and isozyme analyses. The cells reacted with rabbit antimoth serum
but not rabbit antimosquito serum. Chromosome analyses indicated Lepidopteran rather than Dipteran morphology, and three isozyme
systems were confirmative. Any one of these assays would be sufficient to indicate that contamination had occurred and could
be used as a periodic check for identity of cell cultures. Morphology and growth characteristics are also valid criteria to
distinguish between these particular orders of insect cells.
These studies were supported by Grant CA-04953-12 from the National Cancer Institute; General Research Support Grant FR-5582
from the National Institues of Health; and Grant-in-Aid Contract M-43 from the State of New Jersey.
Recipient of Research Career Award 5-K3-16,749. from the National Institutes of Health. 相似文献
109.
Arthur E. Greene Jesse Charney Warren W. Nichols Lewis L. Coriell 《In vitro cellular & developmental biology. Plant》1972,7(5):313-322
Summary Three mosquito cell cultures designated as Suitor's clone ofAedes aegypti, Culiseta inornata, andAedes vexans were shown to be moth by immunological, karyological, and isozyme analyses. The cells reacted with rabbit antimoth serum
but not rabbit antimosquito serum. Chromosome analyses indicated Lepidopteran rather than Dipteran morphology, and three isozyme
systems were confirmative. Any one of these assays would be sufficient to indicate that contamination had occurred and could
be used as a periodic check for identity of cell cultures. Morphology and growth characteristics are also valid criteria to
distinguish between these particular orders of insect cells.
These studies were supported by Grant CA-04953-12 from the National Cancer Institute; General Research Support Grant FR-5582
from the National Institutes of Health; and Grant-in-Aid Contract M-43 from the State of New Jersey.
Recipient of Research Career Award 5-K3-16,749 from the National Institutes of Health. 相似文献
110.
The use of the quantitative nasal culture was investigated as a means of evaluation of new antimicrobial drugs in man. Cyclacillin was somewhat more active in vitro than penicillin G against penicillin G-resistant organisms. Cyclacillin was highly effective in suppressing staphylococci susceptible to penicillin G in nasal carriers but did not suppress staphylococci resistant to penicillin G. Although in previous studies by others cyclacillin was effective in treating mice infected with penicillin G-resistant staphylococci, in the present studies cyclacillin was not effective in suppressing nasal penicillin G-resistant staphylococci in man at doses which markedly suppressed penicillin G-sensitive organisms. 相似文献