全文获取类型
收费全文 | 4583篇 |
免费 | 483篇 |
国内免费 | 1篇 |
出版年
2022年 | 25篇 |
2021年 | 59篇 |
2020年 | 45篇 |
2019年 | 49篇 |
2018年 | 48篇 |
2017年 | 55篇 |
2016年 | 101篇 |
2015年 | 182篇 |
2014年 | 199篇 |
2013年 | 242篇 |
2012年 | 319篇 |
2011年 | 300篇 |
2010年 | 197篇 |
2009年 | 182篇 |
2008年 | 259篇 |
2007年 | 331篇 |
2006年 | 263篇 |
2005年 | 255篇 |
2004年 | 256篇 |
2003年 | 259篇 |
2002年 | 225篇 |
2001年 | 57篇 |
2000年 | 30篇 |
1999年 | 54篇 |
1998年 | 72篇 |
1997年 | 68篇 |
1996年 | 54篇 |
1995年 | 40篇 |
1994年 | 61篇 |
1993年 | 40篇 |
1992年 | 43篇 |
1991年 | 24篇 |
1990年 | 31篇 |
1989年 | 37篇 |
1988年 | 34篇 |
1987年 | 38篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 44篇 |
1983年 | 38篇 |
1982年 | 23篇 |
1981年 | 41篇 |
1980年 | 35篇 |
1979年 | 22篇 |
1978年 | 22篇 |
1977年 | 26篇 |
1976年 | 19篇 |
1975年 | 17篇 |
1973年 | 22篇 |
1970年 | 22篇 |
排序方式: 共有5067条查询结果,搜索用时 62 毫秒
101.
Direct immunoprecipitation and two-dimensional (2D) gel electrophoresis have been used to identify and characterize genetic variation of theH-2K andH-2D regions. Using inbred strains of mice and alloantisera, haplotype-specific polypeptides were defined for five differentH-2 haplotypes. Specific immunoprecipitates prepared from strains of different haplotypes were applied to 2D gels in pairwise combinations to determine whether peptides specific to one haplotype can be distinguished from peptides specific to another. Those haplotype-specific peptides that migrate to unique positions on 2D gels with respect to the positions occupied by haplotype-specific peptides of another haplotype are useful as biochemical genetic markers. Cross-reactivity amongK- andD-region antigens of different haplotypes was identified on 2D gels and found to correlate well with existing data based on serological cross-reactivity. An anti-mouse 2-microglobulin serum was found to be a useful general reagent for immunoprecipitating haplotype-specific H-2 antigens to permit their visualization on 2D gels.Abbrevations used in this paper NP-40
nonidet P-40
- 2D
two-dimensional
- SDS
sodium dodecyl sulfate
- IEF
isoelectric focusing 相似文献
102.
Janet M. Arce Brian A. Naughton Gail A. Kolks Philip Liu Albert S. Gordon Sam J. Piliero 《Prostaglandins & other lipid mediators》1981,21(3):367-377
Prostaglandins A2, E1, E2, methylated E2s and F2α affected erythropoiesis and/or erythropoietin (Ep) production. This action is indicated in the exhypoxic, polycythemic mouse where radioiron incorporations into RBC increased after administration of these compounds. The kidney and liver have been indicated through previous studies, to actively participate in Ep production. By the removal of one of these active sites in a murine system treated with prostaglandins it is shown that a response is reflected in Ep levels. Interference of the action of prostaglandins (PG) is altered by the removal of one of these target sites of Ep production. The erythropoietic responses elicited by PGA2, E1, and perhaps the methylated PGE2s act through the liver whereas PGE2 may operate through a renal pathway for its response. PGF2α reveals no effect on erythropoietic activity and is no different than that observed for vehicle-treated controls. The prostaglandins tested appear to act primarily through the kidney or liver but the possibility exists that some yet undetermined organ site may also be involved. 相似文献
103.
The GABAergic system was investigated in C-6 astrocytoma cells and C-1300 neuroblastoma cells in culture and compared to that in mouse brain. The activities of glutamate decarboxylase, GABA-transaminase, succinic semialdehyde dehydrogenase and glutamate dehydrogenase were measured. In the cultured cells, only glutamate dehydrogenase activity was equal or greater than that of mouse cerebral cortex. Glutamate decarboxylase in both cell lines was 2%, while GABA-transaminase and succinic semialdehyde dehydrogenase activities were less than 20% of those found in brain. In spite of the disparate enzyme activities, GABA, glutamate, and -ketoglutarate concentrations were similar in the cell lines and cerebral cortex. The anticonvulsant drugs sodium valproate and aminooxyacetic acid increased cortical GABA concentrations but either had no effect or decreased GABA in the cells in a complete medium. The convulsant isoniazid decreased GABA in mouse brain but had no effect in either cell line. In the absence of pyridoxal in the medium, some drug effects could be induced in the cultured cells. It is concluded that the differing responses of the GABAergic system in the mouse brain and cell lines may be attributed in part to the fact that the cells do not represent an integrated system and are of tumor origin. 相似文献
104.
Simulated phototropic curvatures caused by differential masking of the cotyledons of de-etiolated seedlings exposed to white light are unconnected with true phototropism. In Cucumis sativus L. and Helianthus annuus L. such curvatures result from a red-light-induced inhibition coming from the exposed cotyledon. True phototropic bending in these species under long-term exposure to fairly high irradiances (as in nature) is a response to blue light. It occurs even when cotyledons are completely covered. These results show that the cotyledons do not perceive the phototropic stimulus and need not be illuminated for phototropism to occur. 相似文献
105.
Detection of Mouse Mammary Tumor Virus RNA in BALB/c Tumor Cell Lines of Nonviral Etiologies 总被引:8,自引:5,他引:3
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jaquelin P. Dudley Janet S. Butel Susan H. Socher Jeffrey M. Rosen 《Journal of virology》1978,28(3):743-752
A complementary DNA (cDNA) probe to mouse mammary tumor virus (MMTV) RNA was synthesized using calf thymus DNA oligonucleotides as a random primer. This probe was then used to study the expression of MMTV RNA in cell lines from BALB/c tumors induced in vivo either spontaneously or in response to viral, chemical, or hormonal stimuli. The cDNA had a length of approximately 400 to 500 nucleotides and specifically hybridized to MMTV RNA and BALB/c lactating mammary gland RNA, but not to Moloney leukemia virus RNA. Calf thymus DNA-primed cDNA could protect 50% of iodinated MMTV RNA from S1 nuclease digestion at cDNA-RNA ratios of 1:1 and 90% of labeled viral RNA at ratios of 10:1. Thermal denaturation of MMTV RNA-cDNA hybrids yielded a T(m) of 88.5 degrees C, indicative of a well-base-paired duplex. Screening of mouse mammary tumor cells for MMTV sequences revealed that three out of five lines of BALB/c origin had undetectable levels of viral RNA (相似文献
106.
Janet H. Ransom Charles H. Evans A. Eric Jones Robert A. Zoon Joseph A. DiPaolo 《Cancer immunology, immunotherapy : CII》1983,15(2):126-130
Summary Immunologic prevention of the carcinogenicity of the diagnostic gamma-emitting radionuclide 99mTechnetium (99mTc) by lymphotoxin was evaluated using an in vivo-in vitro assay of carcinogenesis. Pregnant Syrian golden hamsters received 125–2,300 Ci 99mTc/kg body weight by injection, and 7 days later colonies of morphologically transformed cells were quantitated in vitro. The transformation frequency increased directly with the radionuclide concentration, and cells derived from transformed colonies produced tumors in athymic nude mice. The total absorbed 99mTc dose was 0.20 rad following injection of 250 Ci 99mTc/kg hamster body weight; this compares with an exposure of 0.13 rad following injection of 143 Ci 99mTc/kg body weight in humans. Intravenous injection of purified hamster lymphotoxin immediately after 99mTc caused a dose-dependent reduction in the transformation frequency. Transformation was essentially completely prevented (97%) by injection of 8,000 U of lymphotoxin. Thus, the immune system, through the action of lymphotoxin, has the potential to prevent carcinogenesis induced by gamma-radiation from 99mTc. This emphasizes the importance of considering the recipient's immune and other homeostatic mechanisms as part of a complete diagnostic or therapeutic gamma-radiation regimen. 相似文献
107.
Francis L. Marcrina R.Paul Evans Janet Ash Tobian Donna L. Hartley Don B. Clewell Kevin R. Jones 《Gene》1983,25(1):145-150
A novel plasmid vector that is able to replicate both in Escherichia coli and in Streptococcus sanguis is described. This 9.2-kb plasmid, designated pVA856, carries Cmr, Tcr and Emr determinants that are expressed in E. coli. Only the Emr determinant is expressed in S. sanguis. Both the Cmr and the Tcr of pVA856 may be insertionally inactivated. This plasmid affords several different cleavage-ligation strategies for cloning in E. coli followed by subsequent introduction of chimeras in to S. sanguis. In addition, we have modified a previously described E. coli-S. sanguis shuttle plasmid [pVA838; Macrina et al., Gene 19 (1982) 345–353], so that it is unable to replicate in S. sanguis. The utility of such a plasmid for cloning and selecting sequences enabling autonomous replication in S. sanguis is demonstrated. 相似文献
108.
A procedure for the sequential staining of metaphase cells to provide R-banding, Q-banding and C-banding of chromosomes is described. The combined techniques allow more precise identification of marker chromosomes and more accurate definition of breakpoints in the consistent chromosome translocations that are associated with certain human malignancies. 相似文献
109.
The relative influence of age and weight on the reproductive behaviour of male grey seals Halichoerus grypus 总被引:1,自引:0,他引:1
The breeding behaviour of male grey seals Halichoerus grypus of known age and weight was studied on Sable Island, Nova Scotia. Branded males ranged in age from 8 to 16 years and although there was a positive relationship between age and weight, there was a large overlap between age classes. In general, there was an increase in length of tenure and rates of copulation with increasing male age but this was less marked among males between the ages of 13 and 16 years. Compared to older ones, males of 8 and 12 years were observed at more sites, travelled more extensively around the breeding colony, were transient more frequently and were unable to lie as close to females. There was no correlation between male body weight and either length of tenure or rates of copulation when males of age 8 (the smallest males) were excluded from the analysis. Most agonistic behaviour was made by larger, older males towards smaller, younger ones and appeared to be responsible for the short length of tenure and low reproductive rates of young bulls. 相似文献
110.
Macrocystis pyrifera gametophytes were exposed in batch culture to varying mass concentrations of buried, sewage-contaminated, historically discharged sediment that had been sampled from two sites off Palos Verdes Peninsula, California. Significant gametophytic vegetative growth inhibition was detected in six days, using digital image analysis at sediment loadings ranging from 0.15 to 14.5 g in 500 mL nutrient-enriched seawater. Inhibition declined at low sediment loadings and increased at high loadings as cultures aged. Sediments corresponding to the historic emissions peak taken 2 km from the Joint Water Pollution Control Plant outfall inhibited vegetative growth more than did sediments sampled 13 km distant. Analysis showed elevated aqueous Cd(II), Cr(II) and p,p-DDE concentrations in high sediment-loading culture medium. Inhibition by Zn(II) alone was observed at similar concentrations in other experiments, but synergism or antagonism by other toxicants remains possible. 相似文献