全文获取类型
收费全文 | 1833092篇 |
免费 | 175186篇 |
国内免费 | 1586篇 |
出版年
2021年 | 18523篇 |
2018年 | 20595篇 |
2017年 | 19361篇 |
2016年 | 30179篇 |
2015年 | 43593篇 |
2014年 | 51806篇 |
2013年 | 78034篇 |
2012年 | 53927篇 |
2011年 | 46942篇 |
2010年 | 50264篇 |
2009年 | 49632篇 |
2008年 | 42514篇 |
2007年 | 42349篇 |
2006年 | 43463篇 |
2005年 | 44648篇 |
2004年 | 43393篇 |
2003年 | 40539篇 |
2002年 | 38341篇 |
2001年 | 62269篇 |
2000年 | 60119篇 |
1999年 | 52722篇 |
1998年 | 28794篇 |
1997年 | 28625篇 |
1996年 | 27518篇 |
1995年 | 25736篇 |
1994年 | 25262篇 |
1993年 | 24701篇 |
1992年 | 44183篇 |
1991年 | 42482篇 |
1990年 | 40873篇 |
1989年 | 41018篇 |
1988年 | 37549篇 |
1987年 | 35827篇 |
1986年 | 33682篇 |
1985年 | 35029篇 |
1984年 | 31812篇 |
1983年 | 27873篇 |
1982年 | 24969篇 |
1981年 | 23690篇 |
1980年 | 22165篇 |
1979年 | 28168篇 |
1978年 | 24445篇 |
1977年 | 22794篇 |
1976年 | 21700篇 |
1975年 | 22308篇 |
1974年 | 23595篇 |
1973年 | 23725篇 |
1972年 | 20755篇 |
1971年 | 18847篇 |
1970年 | 16542篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
931.
932.
933.
934.
Bruce R. Dorrbecker Susan H. Mercik Paul A. Kramer 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1984,336(1)
A high-performance liquid chromatographic procedure is reported for reproducibly and sensitively quantitating caffeine and its N-demethylated metabolite paraxanthine in micro-samples. A 5-μm reversed-phase radial compression column and 214-nm fixed wavelength ultraviolet detector were used to attain a sensitivity sufficient to quantitate these compounds at concentratios as low as 80 ng/ml using only 25 μl of sample. The assay is applicable to microliter samples of whole blood, serum, plasma, saliva, amniotic, cerebro-spinal and gastric fluids such as might be obtained in studies involving small animals or neonates. The utility of the assay is illustrated with caffeine and paraxanthine levels measured in several maternal and fetal fluids following constant-rate intravenous infusion of caffeine into a rabbit throughout pregnancy. 相似文献
935.
936.
Chromosome transfer and R-prime formation by an RP4::mini-Mu derivative in Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae, and Proteus mirabilis 总被引:34,自引:0,他引:34
We have introduced into the wide host range conjugative plasmid RP4, a mini-Mu derivative which was known to be able to transpose spontaneously in E. coli K-12, and to induce in such a host several kinds of chromosomal rearrangements including replicon fusions. Unlike RP4, RP4::mini-Mu can mediate the transfer of the host chromosome to a recipient bacterium and generate R primes at high frequencies (10?4 for the transfer of a given marker, 10?5 for the formation of R primes carrying a given marker). Two such RP4::mini-Mu plasmids were introduced into one Salmonella typhimurium strain, one Klebsiella pneumoniae strain, and one Proteus mirabilis strain. Each of these three strains were mated with an E. coli K-12 recipient and transconjugants carrying R primes were recovered in all three cases at frequencies ranging from 5 × 10?6 to 10?7. 相似文献
937.
938.
A double antibody radioimmunoassay technique is described for the measurement of anti-zona antibodies in the peripheral plasma of marmosets actively immunized against intact cow zonae pellucidae. The method has been shown to be a reliable, repeatable indicator of antibody titer, enabling direct comparison of the response obtained between marmosets. This is the first report of a procedure describing the active immunization of a primate against zona antigens, and the first time a radioimmunoassay technique has been used to monitor profiles of anti-cow zona antibody production following active immunization. The method should prove to be a useful tool in the evaluation of zona antigens as agents for immunocontraception. 相似文献
939.
940.
Physicians with an interest in pain have long suggested that the poor complain more and have a higher prevalence of neuroticism than do higher social groups. This assumption was tested by analysing the pain patterns in 500 consecutive patients attending a pain relief clinic. Results implied that scores for presenting pain, anxiety, and depression were similar to all social groups. After treatment scores for residual pain were significantly lower in all social classes, with greatest reduction in classes III, IV, and V. Almost identical results were obtained in a subgroup of patients with cancer but not in a subgroup with sciatica. That patients from the lower social classes have a higher perception of pain and are more neurotic than other group is a myth, probably resulting from poor communication between clinicians and patients of dissimilar socioeconomic class. 相似文献