全文获取类型
收费全文 | 29506篇 |
免费 | 802篇 |
国内免费 | 151篇 |
专业分类
化学 | 19715篇 |
晶体学 | 268篇 |
力学 | 722篇 |
综合类 | 1篇 |
数学 | 4568篇 |
物理学 | 5185篇 |
出版年
2022年 | 255篇 |
2021年 | 307篇 |
2020年 | 415篇 |
2019年 | 407篇 |
2018年 | 301篇 |
2017年 | 283篇 |
2016年 | 580篇 |
2015年 | 511篇 |
2014年 | 615篇 |
2013年 | 1481篇 |
2012年 | 1320篇 |
2011年 | 1695篇 |
2010年 | 930篇 |
2009年 | 791篇 |
2008年 | 1399篇 |
2007年 | 1430篇 |
2006年 | 1413篇 |
2005年 | 1341篇 |
2004年 | 1205篇 |
2003年 | 1012篇 |
2002年 | 998篇 |
2001年 | 435篇 |
2000年 | 432篇 |
1999年 | 371篇 |
1998年 | 333篇 |
1997年 | 385篇 |
1996年 | 441篇 |
1995年 | 345篇 |
1994年 | 332篇 |
1993年 | 392篇 |
1992年 | 356篇 |
1991年 | 343篇 |
1990年 | 278篇 |
1989年 | 259篇 |
1988年 | 269篇 |
1987年 | 336篇 |
1986年 | 281篇 |
1985年 | 396篇 |
1984年 | 429篇 |
1983年 | 318篇 |
1982年 | 385篇 |
1981年 | 415篇 |
1980年 | 350篇 |
1979年 | 351篇 |
1978年 | 375篇 |
1977年 | 319篇 |
1976年 | 297篇 |
1975年 | 308篇 |
1974年 | 291篇 |
1973年 | 260篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
R W Milne R L Nation G D Reynolds A A Somogyi J T Van Crugten 《Journal of chromatography. A》1991,565(1-2):457-464
Improvements to previously reported methods for the determination of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) in human plasma are described. The improved methods involve the use of a solid-phase extraction cartridge and a chromatographic system which uses paired-ion reversed-phase high-performance liquid chromatography with a radially compressed column. Only one cartridge is used to prepare each sample for chromatography and each cartridge may be used for at least fourteen 1-ml plasma samples. The recovery is greater than 85%. The improvements to the method of sample pretreatment and in the chromatographic conditions have allowed determination of morphine, M3G and M6G in human plasma down to 13.3 nmol/l (coefficient of variation = 9.3%), 108 nmol/l (6.6%) and 41 nmol/l (6.7%), respectively, using ultraviolet detection alone. It was shown that all three compounds were stable in plasma for up to 101 weeks when stored at -20 degrees C. 相似文献
92.
A Network Simulation of High-congestion Road-traffic Flows in Cities with Marine Container Terminals
James A. Pope Terry R. Rakes Loren Paul Rees Ingrid W. M. Crouch 《The Journal of the Operational Research Society》1995,46(9):1090-1101
Port cities where marine cargo terminals are located are generally near urban areas characterized by high-congestion road traffic. Changes in cargo traffic volumes into a marine terminal, or in the surrounding traffic arteries, which carry this traffic, can significantly affect the terminal's operations. Conversely, activity at the terminal can have an impact on the traffic levels and congestion for a considerable distance from the terminal. This paper demonstrates a methodology useful for studying the impact of road traffic flows on marine container terminals located in highly congested areas. This model was developed at the request of the Virginia Center for World Trade and was used to answer three planning questions in the port of Hampton Roads, Virginia, USA-what would be the impact of: opening a new section of interstate highway, a projected doubling of container traffic at one terminal, and a daily unit train in the vicinity of another terminal. The problem was made more challenging by limited data-collection funds. None the less, the model was deemed valid by a panel of traffic experts and officials from several major state and private agencies involved in marine traffic management. The model results were subsequently a factor in two major decisions related to terminal management. 相似文献
93.
M. H. Gehlen M. Van der Auweraer F. C. De Schrwer 《Photochemistry and photobiology》1991,54(4):613-618
The luminescence decay of excited probes in micelles in the presence of a Poisson distribution of quenchers is considered under conditions where both probe and quencher within the lifetime of the excited probe may exchange between the micelles. Analytical and numerical results show that the luminescence decay can be expressed by a generalized self convolution product of a multiexponential decay function. 相似文献
94.
T. Van Cauteren J. Ryckebusch B. Metsch H. -R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):613-615
We present some of our results for the electromagnetic properties of excited Σ hyperons, computed within the framework of the Bonn constituent-quark model, which is based on the Bethe-Salpeter approach.
The seven parameters entering the model are fitted against the best-known baryon masses. Accordingly, the results for the
form factors and helicity amplitudes are genuine predictions. We compare with the scarce experimental data available and discuss
the processes in which Σ
*'s may play an important role. 相似文献
95.
Paul Howard 《Mathematical Logic Quarterly》2007,53(3):247-254
Two theorems are proved: First that the statement “there exists a field F such that for every vector space over F, every generating set contains a basis” implies the axiom of choice. This generalizes theorems of Halpern, Blass, and Keremedis. Secondly, we prove that the assertion that every vector space over ?2 has a basis implies that every well‐ordered collection of two‐element sets has a choice function. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
96.
Katharina Habermann Lutz Habermann Paul Rosenthal 《Calculus of Variations and Partial Differential Equations》2007,30(2):137-152
A Yang–Mills theory in a purely symplectic framework is developed. The corresponding Euler–Lagrange equations are derived
and first integrals are given. We relate the results to the work of Bourgeois and Cahen on preferred symplectic connections. 相似文献
97.
98.
Tracy Huziak‐Clark Stephen J. Van Hook Julie Nurnberger‐Haag Lena Ballone‐Duran 《School science and mathematics》2007,107(8):311-324
This article focuses on the impact a collaborative project between university graduate fellows and K‐12 classroom teachers had on improved pedagogy in the classroom and in the future at the university. Nine teams participated in a yearlong professional development project to improve pedagogy and communication skills of the participants. This study shows that the participants, the fellows and the K‐12 teacher partners, made changes in planning, implementation, and even motivation for using inquiry‐based methods in their classroom. External observations of the teams further support the individuals' claims of improved pedagogy using inquiry and impact on student conceptual understanding. The Horizon Classroom Observation instrument was used for these observations. The teams showed an overall increase in scores, as well as overall effective and exemplarily implementation of their planning. The program design, the implementation, and the results of this three‐year study will be elaborated in this article. 相似文献
99.
F. Trandafir P. Heerdt M. Fittipaldi E. Vinck S. Dewilde L. Moens S. Van Doorslaer 《Applied magnetic resonance》2007,31(3-4):553-572
In this work, the high-spin ferric form of the E7Q mutant of human neuroglobin (E7Q-NGB) is studied by X-band continuous-wave electron paramagnetic resonance (CW EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopy. It is shown that the use of matched pulses in the HYSCORE experiment is essential to observe the nitrogen spectral contributions. The validity of approximating the high-spin Fe(III) system (S=5/2) as an effectiveS=1/2 system is tested and the consequences for the HYSCORE simulations are highlighted. Comparative HYSCORE experiments combined with deuterium exchange experiments for aquometmyoglobin and ferric E7Q-NGB clearly show that the heme iron of the latter protein is pentacoordinated, lacking the distal water. Furthermore, CW EPR experiments show that, at high pH, the E10K residue is coordinating to the heme iron in this globin. These observations are corroborated by resonance Raman experiments and could also be reproduced for other E7 mutants of human and mouse neuroglobin. Finally, the proton and nitrogen hyperfine and nuclear quadrupole parameters obtained for ferric E7Q-NGB are discussed in detail. 相似文献
100.
We study (relative) zeta regularized determinants of Laplace type operators on compact conic manifolds. We establish gluing formulae for relative zeta regularized determinants. For arbitrary self-adjoint extensions of the Laplace-Beltrami operator, we express the relative ζ-determinants for these as a ratio of the determinants of certain finite matrices. For the self-adjoint extensions corresponding to Dirichlet and Neumann conditions, the formula is particularly simple and elegant. 相似文献