全文获取类型
收费全文 | 38768篇 |
免费 | 282篇 |
国内免费 | 324篇 |
专业分类
化学 | 16067篇 |
晶体学 | 357篇 |
力学 | 1742篇 |
综合类 | 12篇 |
数学 | 10593篇 |
物理学 | 10603篇 |
出版年
2021年 | 152篇 |
2020年 | 158篇 |
2019年 | 148篇 |
2018年 | 1302篇 |
2017年 | 1549篇 |
2016年 | 888篇 |
2015年 | 703篇 |
2014年 | 634篇 |
2013年 | 1212篇 |
2012年 | 3446篇 |
2011年 | 2730篇 |
2010年 | 2101篇 |
2009年 | 1800篇 |
2008年 | 940篇 |
2007年 | 956篇 |
2006年 | 942篇 |
2005年 | 4707篇 |
2004年 | 4205篇 |
2003年 | 2558篇 |
2002年 | 752篇 |
2001年 | 478篇 |
2000年 | 274篇 |
1999年 | 321篇 |
1998年 | 227篇 |
1997年 | 205篇 |
1996年 | 213篇 |
1995年 | 160篇 |
1994年 | 170篇 |
1993年 | 177篇 |
1992年 | 324篇 |
1991年 | 314篇 |
1990年 | 254篇 |
1989年 | 225篇 |
1988年 | 231篇 |
1987年 | 240篇 |
1986年 | 190篇 |
1985年 | 240篇 |
1984年 | 217篇 |
1983年 | 178篇 |
1982年 | 188篇 |
1981年 | 199篇 |
1980年 | 187篇 |
1979年 | 201篇 |
1978年 | 193篇 |
1977年 | 182篇 |
1976年 | 226篇 |
1975年 | 200篇 |
1974年 | 169篇 |
1973年 | 171篇 |
1972年 | 114篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
81.
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
82.
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
83.
Dorota G?azowska Janusz Matkowski 《Journal of Mathematical Analysis and Applications》2007,331(2):1187-1199
The invariance of the geometric mean G with respect to the Lagrangian mean-type mapping (Lf,Lg), i.e. the equation G○(Lf,Lg)=G, is considered. We show that the functions f and g must be of high class regularity. This fact allows to reduce the problem to a differential equation and determine the second derivatives of the generators f and g. 相似文献
84.
In the paper we indicate an error made in the proof of the main result of the paper [M.A. Darwish, On quadratic integral equation of fractional orders, J. Math. Anal. Appl. 311 (2005) 112-119]. Moreover, we provide correct proof of a slightly modified version of the mentioned result. The main tool used in our proof is the technique associated with the Hausdorff measure of noncompactness. 相似文献
85.
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
86.
In this paper we deal with nonlinear second-order boundary value problems with impulses. The impulsive functions depend implicitly on the different considered variables and the boundary value conditions are nonlinear. In both cases functional dependence on the solution is allowed. The existence results follow from the existence of a pair of well-ordered lower and upper solutions. 相似文献
87.
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
88.
We study linear dynamical systems with multidimensional time in Banach spaces. Using Taylor functional calculus we prove that under additional assumptions hyperbolic systems have shadowing property. 相似文献
89.
S?awomir Solecki 《Topology and its Applications》2007,154(12):2462-2464
Let I0 be the σ-ideal of subsets of a Polish group generated by Borel sets which have perfectly many pairwise disjoint translates. We prove that a Fubini-type theorem holds between I0 and the σ-ideals of Haar measure zero sets and of meager sets. We use this result to give a simple proof of a generalization of a theorem of Balcerzak-Ros?anowski-Shelah stating that I0 on N2 strongly violates the countable chain condition. 相似文献
90.
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