全文获取类型
收费全文 | 5342篇 |
免费 | 158篇 |
国内免费 | 19篇 |
专业分类
化学 | 3463篇 |
晶体学 | 14篇 |
力学 | 247篇 |
数学 | 911篇 |
物理学 | 884篇 |
出版年
2023年 | 43篇 |
2022年 | 147篇 |
2021年 | 147篇 |
2020年 | 122篇 |
2019年 | 111篇 |
2018年 | 87篇 |
2017年 | 105篇 |
2016年 | 193篇 |
2015年 | 164篇 |
2014年 | 161篇 |
2013年 | 288篇 |
2012年 | 305篇 |
2011年 | 333篇 |
2010年 | 192篇 |
2009年 | 184篇 |
2008年 | 317篇 |
2007年 | 318篇 |
2006年 | 262篇 |
2005年 | 282篇 |
2004年 | 191篇 |
2003年 | 193篇 |
2002年 | 147篇 |
2001年 | 62篇 |
2000年 | 57篇 |
1999年 | 54篇 |
1998年 | 42篇 |
1997年 | 40篇 |
1996年 | 65篇 |
1995年 | 53篇 |
1994年 | 42篇 |
1993年 | 44篇 |
1992年 | 32篇 |
1991年 | 31篇 |
1990年 | 34篇 |
1989年 | 38篇 |
1988年 | 30篇 |
1987年 | 45篇 |
1986年 | 30篇 |
1985年 | 48篇 |
1984年 | 44篇 |
1983年 | 26篇 |
1982年 | 28篇 |
1981年 | 33篇 |
1980年 | 35篇 |
1979年 | 36篇 |
1978年 | 19篇 |
1977年 | 31篇 |
1976年 | 14篇 |
1975年 | 18篇 |
1974年 | 14篇 |
排序方式: 共有5519条查询结果,搜索用时 15 毫秒
1.
Journal of Optimization Theory and Applications - Pollution management models of Shallow Lake type identify a well-known class of infinite horizon optimal control problems, characterized by the... 相似文献
2.
3.
Numerical Algorithms - We introduce a modulus-based formulation for vertical linear complementarity problems (VLCPs) with an arbitrary number ? of matrices. This formulation can be used to... 相似文献
4.
Francesco Segatta David M. Rogers Naomi T. Dyer Ellen E. Guest Zhuo Li Hainam Do Artur Nenov Marco Garavelli Jonathan D. Hirst 《Molecules (Basel, Switzerland)》2021,26(2)
A fully quantitative theory of the relationship between protein conformation and optical spectroscopy would facilitate deeper insights into biophysical and simulation studies of protein dynamics and folding. In contrast to intense bands in the far-ultraviolet, near-UV bands are much weaker and have been challenging to compute theoretically. We report some advances in the accuracy of calculations in the near-UV, which were realised through the consideration of the vibrational structure of the electronic transitions of aromatic side chains. 相似文献
5.
Dr. Carla Carrera Dr. Eleonora Cavallari Dr. Giuseppe Digilio Dr. Oksana Bondar Prof. Silvio Aime Dr. Francesca Reineri 《Chemphyschem》2021,22(11):1042-1048
An efficient synthesis of vinyl-[1-13C]pyruvate has been reported, from which 13C hyperpolarized (HP) ethyl-[1-13C]pyruvate has been obtained by means of ParaHydrogen Induced Polarization (PHIP). Due to the intrinsic lability of pyruvate, which leads quickly to degradation of the reaction mixture even under mild reaction conditions, the vinyl-ester has been synthesized through the intermediacy of a more stable ketal derivative. 13C and 1H hyperpolarizations of ethyl-[1-13C]pyruvate, hydrogenated using ParaHydrogen, have been compared to those observed on the more widely used allyl-derivative. It has been demonstrated that the spin order transfer from ParaHydrogen protons to 13C, is more efficient on the ethyl than on the allyl-esterdue to the larger J-couplings involved. The main requirements needed for the biological application of this HP product have been met, i. e. an aqueous solution of the product at high concentration (40 mM) with a good 13C polarization level (4.8 %) has been obtained. The in vitro metabolic transformation of the HP ethyl-[1-13C]pyruvate, catalyzed by an esterase, has been observed. This substrate appears to be a good candidate for in vivo metabolic investigations using PHIP hyperpolarized probes. 相似文献
6.
Vito Gigante Laura Aliotta Maria Beatrice Coltelli Patrizia Cinelli Luigi Botta Francesco Paolo La Mantia Andrea Lazzeri 《Journal of polymer science. Part A, Polymer chemistry》2020,58(23):3264-3282
The development of biodegradable materials for tailored applications, particularly in the field of polymeric films and sheets, is a challenging technological goal as well as a contribution to help protect the environment. Poly(lactic) acid (PLA) is a promising substitute for several oil-based polymers; however, to overcome its thermal and mechanical drawbacks, researchers have developed solutions such as blending PLA with polybutylene adipate terephthalate (PBAT), which is capable of increasing the ductility of the final material. In this study, PLA/PBAT binary blends, with minimum possible content of nonrenewable materials, were examined from processing, thermal, morphological, and rheological perspective. An optimized PLA/PBAT ratio was chosen as the polymeric basis to obtain a biodegradable formulation by adding a biobased plasticizer and appropriate fillers to produce a micrometer film with tailored flexibility and tear resistance. The processing technology involved flat-die extrusion, followed by calendering. The tearing resistance of the produced film was investigated, and the results were compared with literature data. A study on the essential work of fracture was implemented to explore the mode III out-of-plane fracture resistance starting from a trouser tear test. 相似文献
7.
8.
The concept of strong interactions need not be limited to the sector of physics taken by QCD. While this domain is investigated by RHIC, LHC will be able to probe potential new strong interactions simultaneously: Finding the precise mechanism for electroweak symmetry breaking is one of the prime problems of physics. Intricately linked to this point is the question after the true nature or even the existence of the Higgs boson. Here, we present stronly interacting theories providing an explanation for the hierarchy problem and leading to a light composite Higgs boson, favoured by experimental data. Our variation of the standard model is consistent with precision data. We achieve this accordance by using technifermions in a higher representation of their gauge group. Anomaly conditions require at least one extra lepton family for some of the theories whereby they contain a natural dark matter candidate. We can accurately determine the masses of said leptons from experimental data. 相似文献
9.
Ohne Zusammenfassung 相似文献
10.
Kristin Fischer Silvio Prause Stefan Spange Frank Cichos Christian Von Borczyskowski 《Journal of Polymer Science.Polymer Physics》2003,41(11):1210-1218
Solvent‐dependent ultraviolet–visible (UV–vis) absorption and Stokes shifts including strong hydrogen‐bond‐donating (HBD) solvents such as 2,2,2‐trifluoroethanol and 1,1,1,3,3,3‐hexafluoro‐2‐propanol of two coumarine dyes (Co 151 and Co 153) were analyzed with multiple‐square analyses of linear solvation energy relationships and the Kamlet–Taft solvent parameter set to α (HBD capacity), β (hydrogen‐bond‐accepting capacity), and π* (dipolarity/polarizability). The UV–vis absorption and emission spectra of Co 151 and Co 153 were measured when adsorbed on various polysaccharides such as different cellulose batches, carboxymethylcelluloses with different degrees of substitution, and chitine. As a result of this evaluation, Co 153 is recommended as an alternative UV–vis probe for evaluating the dipolarity/polarizability of cellulose and cellulose derivates. Multiple adsorption of Co 153 on Linters cellulose took place indicating a wide‐surface polarity distribution, which makes the determination of a rigid polarity parameter questionable. Thus, fluorescence measurements of adsorbed Co 153 are suitable to detect inhomogenities on a surface but not for the determination of empirical polarity parameters. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1210–1218, 2003 相似文献