全文获取类型
收费全文 | 638598篇 |
免费 | 65954篇 |
国内免费 | 805篇 |
专业分类
705357篇 |
出版年
2018年 | 6819篇 |
2017年 | 6483篇 |
2016年 | 9084篇 |
2015年 | 12073篇 |
2014年 | 14306篇 |
2013年 | 19334篇 |
2012年 | 22607篇 |
2011年 | 23194篇 |
2010年 | 15531篇 |
2009年 | 14085篇 |
2008年 | 20162篇 |
2007年 | 20847篇 |
2006年 | 19550篇 |
2005年 | 18294篇 |
2004年 | 18445篇 |
2003年 | 17303篇 |
2002年 | 16824篇 |
2001年 | 26324篇 |
2000年 | 26410篇 |
1999年 | 20715篇 |
1998年 | 7706篇 |
1997年 | 7655篇 |
1996年 | 7184篇 |
1995年 | 6851篇 |
1994年 | 6404篇 |
1993年 | 6496篇 |
1992年 | 17038篇 |
1991年 | 16973篇 |
1990年 | 16593篇 |
1989年 | 16062篇 |
1988年 | 14943篇 |
1987年 | 14108篇 |
1986年 | 13299篇 |
1985年 | 13177篇 |
1984年 | 10879篇 |
1983年 | 9439篇 |
1982年 | 6930篇 |
1981年 | 6236篇 |
1980年 | 5891篇 |
1979年 | 10207篇 |
1978年 | 8224篇 |
1977年 | 7307篇 |
1976年 | 6843篇 |
1975年 | 7967篇 |
1974年 | 8852篇 |
1973年 | 8606篇 |
1972年 | 7837篇 |
1971年 | 7220篇 |
1970年 | 6220篇 |
1969年 | 6035篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Cloning of genes that suppress an Escherichia coli K-12 alanine auxotroph when present in multicopy plasmids. 总被引:1,自引:1,他引:0 下载免费PDF全文
To facilitate molecular analyses of a previously uncharacterized gene involved in alanine synthesis, attempts were made to clone the wild-type allele of this gene, alaA, with a mini-Mu plasmid element used for in vivo cloning. Seventy-six independent Ala+ plasmids were isolated and characterized. Physiological, enzymological, and restriction endonuclease analyses indicated that three different genes, none of them alaA, were cloned. These genes were avtA+, which encodes the alanine-valine transaminase (transaminase C); tyrB+, which encodes the tyrosine-repressible transaminase (transaminase D); and a previously undescribed gene, called alaB, which encodes an alanine-glutamate transaminase. 相似文献
982.
A A Krichevskaia A I Lukash N V Pushkina I V Shepotinovskaia K B Sherstnev 《Nauchnye doklady vysshe? shkoly. Biologicheskie nauki》1984,(7):23-28
The amide content of total proteins and protein fractions (alpha-, beta-, gamma-cristallins and albuminoid) from cortex and nuclear lens zones of cattle has been investigated. The amide content in proteins of cortex and nuclear lens of young animals (1,5-2 years old) is the same. The decrease of the amide content in the proteins of nuclear lenz zone of old animals (6-12 years old) is due to fraction of readily hydrolysed amides. The data obtained prove the posttranslational desamidation of lens proteins at ageing. beta-Cristallines--the proteins with the highest amides content is exposed to posttranslational desamidation most of all. 相似文献
983.
984.
Eileen M. Proctor Judith L. Isaac-Renton William B. Robertson William A. Black 《CMAJ》1985,133(9):876-878
A survey was done of Canadians who had been interned by the Japanese during World War II to assess the prevalence of latent infection with Strongyloides stercoralis in this group. Packages containing three mail-in kits and a questionnaire were sent to 992 men, 694 (70%) of whom responded. Larvae were found in the stool specimens of four of the respondents. Examination of stool specimens after formalin-ether concentration was the most successful method of detecting Strongyloides larvae. The Baermann concentration technique yielded negative results in all four men. Three of the four cases of strongyloidiasis were detected after sampling of three fecal specimens. In the fourth case additional specimens were requested on the basis of data derived from the questionnaire. The most frequently cited clinical manifestations were abdominal pain, weight loss, diarrhea and rashes. 相似文献
985.
Rats were trained to run spontaneously, without stress, in running wheels. The running activity increased gradually and could reach a plateau of 7 km/night after 3–4 weeks. During the first hour of running in the dark phase the squeak threshold increased significantly and remained high in the morning. The degree of increased threshold was correlated to the amount of running activity. The squeak threshold declined during the following 6 hours of inactivity. A rapid decrease in threshold occurred after naloxone (1–2 mg/kg i.p.). It is suggested that long-lasting muscle exercise (e.g. jogging), acupuncture, and low frequency electrical stimulation of afferent nerve fibres produce discharges in muscle afferents which influence central endorphin mechanics giving analgetic effects. 相似文献
986.
987.
Iu A Blednov Iu L Fedoseev N N Bogdanov M L Gorde? S B Seredenin 《Biulleten' eksperimental'no? biologii i meditsiny》1986,102(9):294-296
The influence of brain acid extract products, isolated by high-performance liquid chromatography on H3-diazepam binding was investigated in synaptosomal membranes of C57BL/6 and BALB/c mice. Fractions with stimulatory and inhibitory activity were isolated. Quantitative and qualitative differences in the effects and structure of ACTH-immunoreactive peptide fractions under study were established. 相似文献
988.
Charles E. Wenner John C. Cheney L. David Tomei 《Journal of cellular biochemistry》1981,15(2):161-168
The introduction of either PGF2α (10?7 M) or TPA (10?7 M) stimulated, ouabain-sensitive 86Rb+ influx at 30 min in postconfluent 3T3-4 mouse fibroblast cultures by 117% and 124%, respectively. Both TPA and PGF2α at these concentrations stimulated the incorporation of 3H-TdR into DNA. TPA had the greatest stimulatory effect, which was similar to that obtained with 10% fetal calf serum. In accord with the idea that modulation of membrane processes such as Na+/K+ pump activity in fibroblasts may reflect important events related to the initiation of DNA synthesis, it was observed that in both 3T3-4 and C3H-1 0T½ cells there were parallel increases in 3H-TdR incorporation and ouabain-sensitive 86Rb+ influxes with 10?7 M TPA, whereas PGF2α stimulated a significant increase in 3H-TdR incorporation in 3T3-4 but not C3H-10T½ cells and only marginal increases in ouabain-sensitive 86Rb+ influx in both. Therefore, although there appears to be a close correlation between Na+/K+ pump activation and subsequent S-phase entry following TPA stimulation, a similar correlation for PGF2α cannot be confirmed. 相似文献
989.
G. Ricci L. Volpi L. Pasquali L. Petrozzi G. Siciliano 《Journal of biological physics》2009,35(4):317-336
Astrocytes have long been considered as just providing trophic support for neurons in the central nervous system, but recently
several studies have highlighted their importance in many functions such as neurotransmission, metabolite and electrolyte
homeostasis, cell signaling, inflammation, and synapse modulation. Astrocytes are, in fact, part of a bidirectional crosstalk
with neurons. Moreover, increasing evidence is stressing the emerging role of astrocyte dysfunction in the pathophysiology
of neurological disorders, including neurodegenerative disease, stroke, epilepsy, migraine, and neuroinflammatory diseases. 相似文献
990.
A. V. Andriyash D. A. Vikhlyaev D. A. Dmitrov A. L. Zapysov A. G. Kakshin I. A. Kapustin E. A. Loboda V. A. Lykov A. V. Potapov V. A. Pronin V. N. Sanzhin V. N. Saprykin A. A. Ugodenko O. V. Chefonov M. N. Chizhkov 《Plasma Physics Reports》2006,32(2):135-137
Results are presented from experimental investigations of the angular distributions and energy spectra of fast ions produced in deuterium polyethylene targets under irradiation by picosecond laser pulses with intensities of up to 2 × 1018 W/cm2 in the SOKOL-P facility. The parameters of ion fluxes were measured by time-of-flight spectrometers based on semiconductor detectors. 相似文献