全文获取类型
收费全文 | 18099篇 |
免费 | 96篇 |
国内免费 | 229篇 |
专业分类
系统科学 | 383篇 |
丛书文集 | 382篇 |
教育与普及 | 72篇 |
理论与方法论 | 60篇 |
现状及发展 | 6258篇 |
研究方法 | 781篇 |
综合类 | 9965篇 |
自然研究 | 523篇 |
出版年
2014年 | 140篇 |
2013年 | 278篇 |
2012年 | 481篇 |
2011年 | 1015篇 |
2010年 | 361篇 |
2009年 | 343篇 |
2008年 | 530篇 |
2007年 | 613篇 |
2006年 | 608篇 |
2005年 | 544篇 |
2004年 | 400篇 |
2003年 | 310篇 |
2002年 | 317篇 |
2001年 | 509篇 |
2000年 | 560篇 |
1999年 | 413篇 |
1992年 | 290篇 |
1991年 | 253篇 |
1990年 | 250篇 |
1989年 | 231篇 |
1988年 | 209篇 |
1987年 | 229篇 |
1986年 | 204篇 |
1985年 | 246篇 |
1984年 | 236篇 |
1983年 | 162篇 |
1982年 | 172篇 |
1981年 | 158篇 |
1980年 | 199篇 |
1979年 | 446篇 |
1978年 | 341篇 |
1977年 | 368篇 |
1976年 | 267篇 |
1975年 | 324篇 |
1974年 | 447篇 |
1973年 | 379篇 |
1972年 | 360篇 |
1971年 | 423篇 |
1970年 | 485篇 |
1969年 | 427篇 |
1968年 | 408篇 |
1967年 | 442篇 |
1966年 | 385篇 |
1965年 | 302篇 |
1959年 | 155篇 |
1958年 | 231篇 |
1957年 | 179篇 |
1956年 | 138篇 |
1955年 | 154篇 |
1954年 | 132篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
103.
104.
Summary The C-11 proton of an aprophine possessing a C-1,2 methylenedioxy group falls relatively upfield between 7.47 and 7.86. Additionally, the i.c.s. for the two protons of the methylenedioxy group is large (4–12 Hz). The presence of a methylenedioxy at C-3,4 in a phenanthrene alkaloid also results in an upfield shift ( 8.95–9.00) of the C-5 proton.This project was supported by NIH research grant No. HL-12971, awarded by the National Heart and Lung Institute, PHS/DHEW. 相似文献
105.
Summary Adenylate kinase activity of intact mitochondria is strongly inhibited by Ap5A, i.e.p
1,p
5-Di (adenosine-5-) pentaphosphate, whereas oxidative phosphorylation is not affected. Therefore, Ap5A is a useful tool to distinguish between oxidative and non oxidative ATP generating reactions.Acknowledgment. The generous support of Prof. Dr.Walther Lamprecht is gratefully acknowledged. J. L. thanks the Stipendienfonds des Verbandes der Chemische Industrie for a scholarship. 相似文献
106.
Summary Tryptic treatment of muscle thick filaments reveals the underlying backbones of aggregatedl-meromyosin as a coli of 3 secondary filaments (helical repeat 130 nm) each in turn a coli of a 3 finer ones. 相似文献
107.
R. G. G. Andersson H. J. Arnqvist L. Lundholm 《Cellular and molecular life sciences : CMLS》1976,32(5):601-602
Summary The incorporation of leucice-14C into protein in bovine mesenteric arteries was augmented by cyclic GMP (10–3
M) and decreased by cyclic AMP (10–3
M). There was no effect of 5 AMP (10–3
M). The phosphodiesterase inhibiting drugs theophylline (10–3
M) and papaverine (5×10–5 g/ml) both decreased the leucine-14C incorporation.We are indebted to Mrs.Lena Burlin for hear assistance. Finacial support has been provided by the Swedish State Medical Research Council (No. 04X-101X-4498). 相似文献
108.
Progress in the study of tectophysicochemistry 总被引:1,自引:0,他引:1
LǖGuxian 《科学通报(英文版)》2003,48(11):1069-1079
Tectophysicochemistry is a research area that deals with the interrelations between physical and chemical changes of crustal materials caused by tectonism. A given tectonic force may be resolved into two parts: homogeneous stress and differential stress. Homogeneous stress refers to isotopic pressure, which is superimposed on the original pressure and affects the equilibrium of various chemical reactions. It is also a factor that influences petrogenesis,metallogenesis and metamorphism. Differential stress is commonly produced when external forces act on a given solid body. It may cause deformation of crustal materials and generate various kinds of structural features. Tectophysicochemistry pays special attention to pressure, temperature and other physicochemical conditions produced or induced by tectonism and studies the influences of additional tectonic parameters on various chemical equilibria, so it gradually develops into an independent area of science. 相似文献
109.
吕明玉 《渝西学院学报(自然科学版)》2003,2(4):65-67
本针对大学预科班学生的特点,从大学预科化学课程的基本目的和要求出发,讨论大学预科化学课程教学中应注意的问题. 相似文献
110.
To ensure reliable land vehicle positioning, the Global Positioning System (GPS) is one of the best techniques commonly used in present-day positioning systems. However, GPS signals are not available if line of sight with the satellites is lost. In this respect, the addition of the Dead Reckoning (DR) method to complement the GPS unit would enhance the reliability of land vehicle positioning system. For implementing the DR method, the magnetic sensor and accelerometer are used for obtaining heading and velocity or distance information. Calibration of two sensors' dynamic model and DR algorithm are also introduced in this paper. The test result utilizing the GPS and DR methods is analyzed in this paper. It utilize spositioning information from GPS receiver when GPSsignal is available, otherwise DR is started to compensate GPS outage with the GPS output as the original point. The results showed that the error in east and north produced by the DR algorithm for a short time interval can be limitedwithin an acceptable range. 相似文献