全文获取类型
收费全文 | 25890篇 |
免费 | 51篇 |
国内免费 | 75篇 |
专业分类
系统科学 | 128篇 |
丛书文集 | 485篇 |
教育与普及 | 59篇 |
理论与方法论 | 94篇 |
现状及发展 | 11619篇 |
研究方法 | 1031篇 |
综合类 | 12290篇 |
自然研究 | 310篇 |
出版年
2012年 | 300篇 |
2011年 | 617篇 |
2008年 | 361篇 |
2007年 | 426篇 |
2006年 | 441篇 |
2005年 | 444篇 |
2004年 | 554篇 |
2003年 | 419篇 |
2002年 | 413篇 |
2001年 | 792篇 |
2000年 | 778篇 |
1999年 | 539篇 |
1994年 | 339篇 |
1992年 | 475篇 |
1991年 | 386篇 |
1990年 | 415篇 |
1989年 | 391篇 |
1988年 | 358篇 |
1987年 | 389篇 |
1986年 | 441篇 |
1985年 | 557篇 |
1984年 | 404篇 |
1983年 | 365篇 |
1982年 | 321篇 |
1981年 | 333篇 |
1980年 | 348篇 |
1979年 | 829篇 |
1978年 | 714篇 |
1977年 | 628篇 |
1976年 | 498篇 |
1975年 | 562篇 |
1974年 | 735篇 |
1973年 | 603篇 |
1972年 | 657篇 |
1971年 | 762篇 |
1970年 | 964篇 |
1969年 | 743篇 |
1968年 | 729篇 |
1967年 | 715篇 |
1966年 | 627篇 |
1965年 | 503篇 |
1964年 | 151篇 |
1959年 | 260篇 |
1958年 | 442篇 |
1957年 | 317篇 |
1956年 | 245篇 |
1955年 | 236篇 |
1954年 | 244篇 |
1953年 | 127篇 |
1948年 | 175篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Summary An intermediate stage between the elementary and the initial bodies of theRickettsiella genus is defined as the beginning of an intracellular cycle. It is characterized by several structural changes in the dense elementary body: the cytoplasm becomes less electron-dense; thus, the nucleoid and the ribosomes are visible. The inner layer of the cell-wall becomes progressively clearer and the trilamellar structure of the inner and outer membranes appears distinctly. Preinitial body is proposed as name of this stage of development. 相似文献
192.
Summary A new norsesquiterpene aldehyde, polygonal and a new sesquiterpene hemiacetal, isodrimeninol having drimane skeleton have been isolated from the seed ofPolygonum hydropiper, and their structures have been established to be1 and5. Polygonal showed pungency and plant growth inhibitory activity. 相似文献
193.
Summary A histochemical study has been made of the main cranial muscles which produce ventilation movements of the rainbow trout. It is shown that a greater proportion of red(aerobic) fibres is present in those muscles known to be active during shallow ventilation than those which become active at greater ventilation volumes. An ordered recruitment of red, pink and white fibres within these muscles is also likely.This work was carried out when I.A. Johnston was holding an NERC Post-Doctoral Research Fellowship (1973–75). 相似文献
194.
M. M. Casellato G. Lugaro G. Cornalba G. Carrea R. Niada 《Cellular and molecular life sciences : CMLS》1979,35(6):784-785
Summary The human urinary glycoprotein with gastric antisecretory activity displays a marked blood-group activity corresponding to the blood-group of the subject examined. Several studies exclude the possibility that the activity is due to contaminants. 相似文献
195.
Chikkadevaiah Shanta R. Hiremath G. Shivashankar 《Cellular and molecular life sciences : CMLS》1979,35(2):171-172
Summary Trigenic ratios have been reported for the first time for the following characters: Habit of the plant, inflorescence type, pod form and pod colour. The first two characters show the presence of 3 common genes and the latter ones are independent.Acknowledgment. The authors are grateful to Dr N.P. Patil, Director of Research, University of Agricultural Sciences, Hebbal, Bangalore, for his encouragement in the course of this study. 相似文献
196.
G. Bianchi Elisabetta Lupotto S. Russo 《Cellular and molecular life sciences : CMLS》1979,35(11):1417-1417
Summary The epicuticular wax of rice, varietyRibe, comprised n-alkanes, esters, aldehydes and free alcohols. The nalkanes contained 4 major chain lengths, C27, C29, C31 and C33. Triacontanal and dotriacontanal were the major aldehydes. Octacosanol comprised 89% of the free alcohols. The esters were mainly esters of C16 to C24 acids with C22 to C30 alcohols.This research was supported by the Consiglio Nazionale delle Ricerche, Rome. 相似文献
197.
T. Saito T. Nohno H. Yoshida H. Yokoya 《Cellular and molecular life sciences : CMLS》1979,35(5):696-699
Summary Trans-4-hydroxy-3-methoxycinnamic acid (ferulic acid, FA) antagonized the effect of exogenous androgens on the ventral prostate (VP) in castrated rats as well as the effect of endogenous androgens in intact rats. FA, however, had no effect on the seminal vesicles (SV) and levator ani muscle (LAM), nor oestrogenic effect in female rats and mice. FA did not antagonize the receptor binding of testosterone nor inhibit the conversion of testosterone into 5-dihydrotestosterone (DHT).Supported in part by the project fund (grant 53-403) of Kawasaki Medical School.The authors would like to thank the Central Laboratory, Sankyo Pharmaceutical Co., Tokyo, for supplying 19-nortestosterone-17-ferulate. 相似文献
198.
A. Scriabine C. T. Ludden L. S. Watson J. M. Stavorski G. Morgan J. J. Baldwin 《Cellular and molecular life sciences : CMLS》1979,35(5):653-655
Summary 2 new 4-trifluoromethylimidazole derivatives were found which lowered mean arterial pressure in renal and spontaneously hypertensive (SH) rats by the oral route. In SH rats, compounds A and B were 0.1 and 0.3 times, respectively, as potent as hydralazine. No tolerance development was observed in SH rats with either compound over a 1-week period. In anesthetized dogs, both compounds lowered arterial pressure and peripheral vascular resistance but increased cardiac output. By intraarterial administration, both compounds increased femoral arterial blood flow. These findings represent discovery of a new class of vasodilator drugs.Deceased, May 31, 1978. 相似文献
199.
H. Yoshida M. Sato R. Kasukawa T. Yoshida 《Cellular and molecular life sciences : CMLS》1979,35(5):676-678
Summary Properties of vascular permeability factor in native human sera (PF/Nat) showed close similarities with those of necrotizing factor. Time course studies revealed that skin necrosis could be initiated by enhanced vascular permeability.Acknowledgment. The authors wish to thank Prof. H. Hayashi, Kumamoto University for encouragement and discussions. 相似文献
200.
Summary Na+ and K+ effects on the resting cellular membrane potential of desheathed ganglia of theBombyx mori L. ventral nerve cord have been studied. The cells are depolarized by high concentrations of external potassium ions in the same way as in vertebrates, mollusca and crustacean cells. The possibility that the behaviour of the resting potential is not only influenced by the potassium equilibrium potential, but also by the conductances to other ions, is discussed.The authors are indebted to Prof V. Capraro, Drs B. Giordana and F. Sacchi for helpful comments and criticism. 相似文献