全文获取类型
收费全文 | 38553篇 |
免费 | 129篇 |
国内免费 | 149篇 |
专业分类
系统科学 | 180篇 |
丛书文集 | 537篇 |
教育与普及 | 63篇 |
理论与方法论 | 132篇 |
现状及发展 | 16450篇 |
研究方法 | 1568篇 |
综合类 | 19172篇 |
自然研究 | 729篇 |
出版年
2013年 | 345篇 |
2012年 | 551篇 |
2011年 | 1271篇 |
2010年 | 242篇 |
2008年 | 634篇 |
2007年 | 797篇 |
2006年 | 740篇 |
2005年 | 765篇 |
2004年 | 795篇 |
2003年 | 674篇 |
2002年 | 705篇 |
2001年 | 1283篇 |
2000年 | 1228篇 |
1999年 | 768篇 |
1992年 | 727篇 |
1991年 | 557篇 |
1990年 | 618篇 |
1989年 | 607篇 |
1988年 | 569篇 |
1987年 | 571篇 |
1986年 | 630篇 |
1985年 | 778篇 |
1984年 | 569篇 |
1983年 | 503篇 |
1982年 | 432篇 |
1981年 | 440篇 |
1980年 | 513篇 |
1979年 | 1243篇 |
1978年 | 953篇 |
1977年 | 922篇 |
1976年 | 753篇 |
1975年 | 770篇 |
1974年 | 1147篇 |
1973年 | 930篇 |
1972年 | 1002篇 |
1971年 | 1125篇 |
1970年 | 1522篇 |
1969年 | 1150篇 |
1968年 | 1069篇 |
1967年 | 1025篇 |
1966年 | 993篇 |
1965年 | 709篇 |
1964年 | 212篇 |
1959年 | 370篇 |
1958年 | 689篇 |
1957年 | 474篇 |
1956年 | 372篇 |
1955年 | 352篇 |
1954年 | 376篇 |
1948年 | 258篇 |
排序方式: 共有10000条查询结果,搜索用时 640 毫秒
261.
H. Watanabe J. A. Menzies J. C. K. Loo 《Cellular and molecular life sciences : CMLS》1981,37(8):883-884
Summary Isonicotinic acid hydrazide (isoniazid) was shown to react readily with 17-ethinyl-17-hydroxyestr-4-en-3-one (norethindrone) to form the isonicotinyl hydrazone of the steroid under conditions likely to exist in the stomach. The hydrazone was detected in guinea-pig, but not rat, plasma following its oral administration. Rat liver tissue metabolized the compound more rapidly than guinea-pig liver in vitro which probably accounts for the failure to detect the hydrazone in rat plasma. 相似文献
262.
D. Sabourault Françoise Bauché Y. Giudicelli J. Nordmann R. Nordmann 《Cellular and molecular life sciences : CMLS》1981,37(3):227-229
Summary After 3 weeks of continuous ethanol intoxication by inhalation, the maximal number and affinity of the -and -receptors of rat heart were unchanged. These data indicate that adrenergic receptor disturbances are not involved in the mechanism of chronic ethanol-induced triglyceride deposition in the heart.Acknowledgments. This work was supported by grants from the Institut National de la Santé et de la Recherche Médicale. We wish to thank Mr M. Clément for skilled technical assistance in performing chronic ethanol inhalation treatments. 相似文献
263.
264.
Summary Food ingestion of male guinea-pigs was restricted to 10 g/day. Total carnitine content of liver of the underfed animals fell to 3.75 moles per liver (46.1% of control). Serum level of total carnitine was 35.0 nmoles/ml (64.4%) in the underfed animals while they developed high ketonemia, 384.2 nmoles/ml (555.2%). In restricted animals the carnitine levels also decreased in the muscles. 相似文献
265.
Summary Thymidylate synthetase (methylenetetrahydrofolate: 2-deoxyuridine-5-monophosphate C-methyltransferase; EC 2.1.1.45) from neonatal mouse liver has been purified 714-fold by affinity chromatography on aminohexylsepharose bound 10-methyl-5,8-dideazafolate.Supported by grant CA22754, awarded by the National Cancer Institute, DHEW. 相似文献
266.
G. Cimino A. Crispino S. De Rosa S. De Stefano G. Sodano 《Cellular and molecular life sciences : CMLS》1981,37(9):924-926
Summary Several high molecular weight polyacetylenes have been isolated from the spongePetrosia ficiformis found in dark caves. These compounds are related to, but different from, the polyacetylenes isolated from the same sponge living in its usual habitat.This work is a part of the Progetto finalizzato per l'Oceanografia e i Fondi Marini, CNR, Roma.The authors thank Mr G. Scognamiglio for the HPLC work, Mr C. Di Pinto for the NMR spectra and Mr G. Villani for the collection of the sponge. 相似文献
267.
Nicoletta Crespi-Perellino A. Guicciardi A. Minghetti C. Spalla 《Cellular and molecular life sciences : CMLS》1981,37(3):217-218
Summary
Claviceps purpurea 275 F.I. fed with -aminobutyric acid produces ergostine with the corresponding -hydroxy--aminoacid undiluted by endogenous aminoacid. Almost all the -aminobutyric acid not incorporated into the ergostine remains unchanged in the medium. The significance of these results in the biosynthesis of ergot alkaloids is discussed. 相似文献
268.
Summary A simple device is described, which permits us to quantify several parameters of spontaneous behaviour of small animals. Using this device with mice we obtained statistically satisfactory results, showing a strong genetic influence on the behavioural characteristics tested.We wish to thank Mr R. Laplace for technical help, Mr J. P. Arnould for electronic work as well as I.N.S.E.R.M.-SCR 3. 相似文献
269.
S. A. Karuppaswamy 《Cellular and molecular life sciences : CMLS》1977,33(6):735-736
Summary The purified chitin from the cuticle of a pentastomid was examined by X-ray method. The X-ray photograph discloses that the chitin in question is of -type. Since the arthropod cuticle contains -chitin, it is suggested that Pentastomida may be considered an independent phylum.Thanks are due to Prof. Dr. G. Sundara Rajulu for guidance and encouragement. 相似文献
270.
For the identification of a peptidyl principle inducing sexual agglutination in the yeast, 2 supposed hexapeptides (1a, b) were synthesized by the conventional method. The 1a (H-Arg-Gly-Pro-Phe-Pro-Ile-OH) revealed complete identity with the natural peptide in TLC, MS and biological property on agglutination. The 1b showed the sexual agglutinability in the same degree as 1a, though distinct differences were observed in the chemical data. Both 1a and 1b had a strong bitter taste. 相似文献