全文获取类型
收费全文 | 12727篇 |
免费 | 386篇 |
国内免费 | 46篇 |
专业分类
化学 | 8605篇 |
晶体学 | 72篇 |
力学 | 389篇 |
综合类 | 1篇 |
数学 | 1734篇 |
物理学 | 2358篇 |
出版年
2023年 | 83篇 |
2022年 | 300篇 |
2021年 | 379篇 |
2020年 | 235篇 |
2019年 | 258篇 |
2018年 | 217篇 |
2017年 | 219篇 |
2016年 | 506篇 |
2015年 | 357篇 |
2014年 | 422篇 |
2013年 | 748篇 |
2012年 | 850篇 |
2011年 | 905篇 |
2010年 | 641篇 |
2009年 | 598篇 |
2008年 | 809篇 |
2007年 | 780篇 |
2006年 | 629篇 |
2005年 | 593篇 |
2004年 | 514篇 |
2003年 | 458篇 |
2002年 | 368篇 |
2001年 | 205篇 |
2000年 | 186篇 |
1999年 | 141篇 |
1998年 | 125篇 |
1997年 | 108篇 |
1996年 | 146篇 |
1995年 | 115篇 |
1994年 | 106篇 |
1993年 | 84篇 |
1992年 | 76篇 |
1991年 | 73篇 |
1990年 | 75篇 |
1989年 | 65篇 |
1988年 | 58篇 |
1987年 | 50篇 |
1986年 | 49篇 |
1985年 | 76篇 |
1984年 | 72篇 |
1983年 | 46篇 |
1982年 | 48篇 |
1981年 | 51篇 |
1980年 | 55篇 |
1979年 | 37篇 |
1978年 | 45篇 |
1977年 | 22篇 |
1976年 | 24篇 |
1975年 | 32篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Manuel Fernández-López Eduardo García-Río Demir N. Kupeli 《Annals of Global Analysis and Geometry》2002,21(1):1-13
A characterization of time functions on a spacetime is made by using theMöbius equation. It is shown that a time function characterized in this wayyields past timelike geodesic incompleteness and local Lorentzian warpedproduct decomposition of spacetime, provided that the stress-energy tensoris a fluid. Also, by imposing additional assumptions on the stress-energytensor and global analytic structure of the spacetime, more restrictivedecompositions closer to Robertson–Walker spacetimes are obtained. 相似文献
73.
Roberto Bassani 《Meccanica》2006,41(4):375-389
S. Earnshaw, a mathematical physicist born in England two centuries ago, was the author of studies on the transmission of
sound and light. His theory on the transmission of light by “detached particles” has also influenced some studies on the stability
of bodies in potential fields, particularly studies on the levitation of permanent magnets, i.e. on passive magnetic levitation.
This theorem was so well known that even Maxwell mentioned it, and is today cited almost as an axiom in the ambit of passive
magnetization. However, what is less well known is that the theory actually only relates to magnetostatics. In this paper,
the mathematic model of the theory that refers to stability is outlined, along with some works that refer to it, in particular
those on passive magnetic levitation. It is then pointed out that spaces of low instability exist in magnetostatics, and that
stability may exist in the magneto-stationary and in magneto-dynamic ambit. 相似文献
74.
Esperanza Salfrn Carlos Seoaneb Margarita Surez Yamila Verdecia Amaury Alvarez Estael Ochoa Roberto Martínez‐Alvarez Nazario Martín 《Journal of heterocyclic chemistry》2004,41(4):509-516
Novel 4‐amino‐6‐aryl‐2‐phenylpyrimidine‐5‐carbonitriles have been prepared in one step procedure from the readily available 4‐aryl‐2‐amino‐3‐cyano‐5,6,7,8‐tetrahydro‐7,7‐dimethyl‐5‐oxo‐4H‐benzopyrans. The mass spectroscopy study under EI conditions shows molecular peaks with high intensity corresponding to the loss of benzonitrile from the C2 position of the pyrimidine ring. Semiempirical (AMI and PM3) and ab initio HF/6–31G* calculations reveal a favored distorted geometry where the three rings are not in the same plane. 相似文献
75.
Roberto Ballini Dennis Fiorini Maria Victoria Gil Alessandro Palmieri 《Tetrahedron》2004,60(12):2799-2804
Nitroalkanes have been found to give good yields in Michael and nitroaldol (Henry) reactions by the use of a catalytic amount (10 mol%) of CTAOH, at room temperature and under solvent free conditions and in very short reaction times. The methods do not need a large excess of the nitroalkanes and show good chemoselectivity toward further functionalities. 相似文献
76.
We prove that, under the assumption of the Generalized Riemann Hypothesis, the exponent of the ideal class group of a CM-field
goes to infinity with its absolute discriminant. This gives a positive answer to a question raised by Louboutin and Okazaki
[4].
Received September 10, 2001; in revised form April 5, 2002 相似文献
77.
78.
This study demonstrates the separation of active ingredients in acne formulations (salicylic acid, cloramphenicol and resorcinol in presence of azulene) by capillary zone electrophoresis. Factors affecting their separations were the buffer pH and concentration, applied voltage, sample preparation, and presence of additives. Optimun results were obtained with a 50 mM sodium tetraborate-50 mM sodium phosphate, pH 9.0. The carrier electrolyte gave baseline separation with good resolution, short migration times (<6 min), great reproducibility and accuracy. Calibration plots were linear over at least three orders of magnitude of analyte concentrations, the lower limits of detection being within the range 0.39-1.25 μg ml−1. The procedure was fast and reliable and commercial pharmaceuticals could be analysed without prior sample clean-up procedure. 相似文献
79.
Given a smooth Lagrangian path, both in the finite and in the infinite dimensional (Fredholm) case, we introduce the notion of partial signatures at each isolated intersection of the path with the Maslov cycle. For real-analytic paths, we give a formula for the computation of the Maslov index using the partial signatures; a similar formula holds for the spectral flow of real-analytic paths of Fredholm self-adjoint operators on real separable Hilbert spaces. As applications of the theory, we obtain a semi-Riemannian version of the Morse index theorem for geodesics with possibly conjugate endpoints, and we prove a bifurcation result at conjugate points along semi-Riemannian geodesics. To cite this article: R. Giambò et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献
80.
Isabel Brandariz José L. Barriada Teresa Vilari?o Manuel E. Sastre de Vicente 《Monatshefte für Chemie / Chemical Monthly》2004,343(6):1475-1488
Several reported procedures for calibrating glass electrodes in proton concentration are compared. Some recommendations for non-experts are also given. The examined procedures can be classified into two broad categories, namely: those based on direct potential difference measurements of solutions of known proton concentration and those that use one or several pH standards to calibrate the electrode and subsequently measure the pH of solutions containing known proton concentrations. With a single buffer, the two types of procedures lead to equivalent results. However, if two pH buffers are used, the slope of the calibration graph in proton concentration will differ from the real electrode slope to an extent proportional to the difference between the liquid junction potentials of the two buffers. Therefore, any other method is preferable under these circumstances. 相似文献