全文获取类型
收费全文 | 4039篇 |
免费 | 127篇 |
国内免费 | 21篇 |
专业分类
化学 | 2986篇 |
晶体学 | 12篇 |
力学 | 79篇 |
数学 | 559篇 |
物理学 | 551篇 |
出版年
2022年 | 22篇 |
2021年 | 42篇 |
2020年 | 45篇 |
2019年 | 50篇 |
2018年 | 33篇 |
2017年 | 25篇 |
2016年 | 90篇 |
2015年 | 111篇 |
2014年 | 81篇 |
2013年 | 154篇 |
2012年 | 204篇 |
2011年 | 247篇 |
2010年 | 182篇 |
2009年 | 123篇 |
2008年 | 228篇 |
2007年 | 215篇 |
2006年 | 214篇 |
2005年 | 211篇 |
2004年 | 140篇 |
2003年 | 121篇 |
2002年 | 126篇 |
2001年 | 65篇 |
2000年 | 81篇 |
1999年 | 71篇 |
1998年 | 62篇 |
1997年 | 75篇 |
1996年 | 66篇 |
1995年 | 62篇 |
1994年 | 55篇 |
1993年 | 68篇 |
1992年 | 62篇 |
1991年 | 28篇 |
1990年 | 37篇 |
1989年 | 31篇 |
1988年 | 38篇 |
1987年 | 41篇 |
1986年 | 35篇 |
1985年 | 62篇 |
1984年 | 27篇 |
1983年 | 32篇 |
1982年 | 43篇 |
1980年 | 44篇 |
1978年 | 29篇 |
1977年 | 40篇 |
1976年 | 23篇 |
1974年 | 23篇 |
1973年 | 21篇 |
1972年 | 25篇 |
1971年 | 22篇 |
1969年 | 23篇 |
排序方式: 共有4187条查询结果,搜索用时 0 毫秒
41.
Konrad Hindelang Alexander Kronast Dr. Sergei I. Vagin Prof. Bernhard Rieger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(25):8244-8252
For the first time, the adaptability of the C?C double bond as a versatile precursor for the postsynthetic modification (PSM) of microporous materials was extensively investigated and evaluated. Therefore, an olefin‐tagged 4,4′‐bipyridine linker was synthesized and successfully introduced as pillar linker within a 9,10‐triptycenedicarboxylate (TDC) zinc paddle‐wheel metal–organic framework (MOF) through microwave‐assisted synthesis. Different reactions, predominately used in organic chemistry, were tested, leading to the development of new postsynthetic reactions for the functionalization of solid materials. The postsynthetic oxidation of the olefin side groups applying osmium tetroxide (OsO4) as a catalyst led to the formation of a microporous material with free vicinal diol functionalities. The epoxidation with dimethyldioxirane (DMDO) enabled the synthesis of epoxy‐functionalized MOFs. In addition to that, reaction procedures for a postsynthetic hydroboration with borane dimethyl sulfide as well as a photoinduced thiol–ene click reaction with ethyl mercaptan were developed. For all of these PSMs, yields of more than 90 % were obtained, entirely maintaining the crystallinity of the MOFs. Since the direct introduction of the corresponding groups by means of pre‐synthetic approaches is hardly possible, these new PSMs are useful tools for the functionalization of porous solids towards applications such as selective adsorption, separation, and catalysis. 相似文献
42.
The ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) was successfully used as alternative solvent for native chemical ligation of peptide fragments to produce model peptide LYRAXCRANK (X = G, A, L, N, Q, K, and F). The commonly used buffer system including thiol additives such as thiophenol and benzyl mercaptan can be replaced by the nontoxic ionic liquid [C2mim][OAc]. In addition to improving the solubility of the peptides in [C2mim][OAc], yields and rates of the ligation reactions were found to be efficiently enhanced. 相似文献
43.
Bettina Lorantfy Tibor Renkecz Cosima Koch George Horvai Bernhard Lendl Christoph Herwig 《Analytical and bioanalytical chemistry》2014,406(9-10):2421-2432
Extreme halophilic archaea are a yet unexploited source of natural carotenoids. At elevated salinities, however, material corrosivity issues occur and the performance of analytical methods is strongly affected. The goal of this study was to develop a method for identification and downstream processing of potentially valuable bioproducts produced by archaea. To circumvent extreme salinities during analysis, a direct sample preparation method was established to selectively extract both the polar and the nonpolar lipid contents of extreme halophiles with hexane, acetone and the mixture of MeOH/MTBE/water, respectively. Halogenated solvents, as used in conventional extraction methods, were omitted because of environmental considerations and potential process scale-up. The HPLC-MS/MS method using atmospheric pressure chemical ionization was developed and tuned with three commercially available C40 carotenoid standards, covering the wide polarity range of natural carotenoids, containing different number of OH-groups. The chromatographic separation was achieved on a C30 RP-HPLC column with a MeOH/MTBE/water gradient. Polar lipids, the geometric isomers of the C50 carotenoid bacterioruberin, and vitamin MK-8 were the most valuable products found in bioreactor samples. In contrast to literature on shake flask cultivations, no anhydrous analogues of bacterioruberin, as by-products of the carotenoid biosynthesis, were detected in bioreactor samples. This study demonstrates the importance of sample preparation and the applicability of HPLC-MS/MS methods on real samples from extreme halophilic strains. Furthermore, from a biotechnological point-of-view, this study would like to reveal the relevance of using controlled and defined bioreactor cultivations instead of shake flask cultures in the early stage of potential bioproduct profiling. 相似文献
44.
Gas thrust bearings are often used in low-load applications, e.g. in air cycle machines, in micro gas turbines or in rotor systems for fuel cell applications, to support a shaft in axial direction. The pressure and temperature distribution in a gas thrust bearing pad are described by the generalized Reynolds equation according to Dowson and the 3D energy equation. In this paper, two different approaches are presented in order to reduce the dimension of the governing nonlinear integro-differential equation system and in order to stabilize the solution process. In the first reduction approach, the temperature in the fluid is averaged across the fluid film according to Lee and Kim. In the second approach, Legendre polynomials are used to approximate temperature, density and fluidity across the fluid film according to Elrod, Brewe and Moraru. The reduction techniques are compared with respect to numerical efficiency, accuracy and convergence behavior. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
45.
46.
Ioku Norisuke Ruf Bernhard Terraneo Elide 《Mathematical Physics, Analysis and Geometry》2015,18(1):1-19
We consider a semilinear heat equation with exponential nonlinearity in ?2. We prove that local solutions do not exist for certain data in the Orlicz space exp L 2(?2), even though a small data global existence result holds in the same space exp L 2(?2). Moreover, some suitable subclass of exp L 2(?2) for local existence and uniqueness is proposed.
相似文献47.
Compounds have been devised whose supportive actions make them important adjuvants in the priming of photosensitization to selectively target cancer cells. Here, we highlight the paper by Maytin and Hasan in this issue of Photochemistry & Photobiology, which describes adjuvants methotrexate, 5-fluorouracil, vitamin D and its analogs leading to improved photodynamic therapy outcome. These small molecule adjuvants act by different mechanisms to enhance the cytotoxicity in tumor cells and the therapeutic effect in cancers. These findings add to the list of strategies for enhancement of photodynamic therapy. 相似文献
48.
Adnan S. Abu-Surrah Gabriele Eckert Wolfgang Pechhold Wolfgang Wilke Bernhard Rieger 《Macromolecular rapid communications》1996,17(8):559-565
Soluble propene/ethene/CO terpolymers (EPEC) with ultrahigh molecular weight (up to 1.2 × 106 g/mol) were prepared by the use of dicationic palladium(II) phosphine catalysts and an optimized amount of water as activator. When the molar ratio of ethene/CO to propene/CO is below 50 mol-%, the terpolymers are thermoplastic elastomers with excellent properties. Above this ratio the terpolymers are crystalline thermoplastics. The ultrahigh molecular weight elastomers are highly soluble in organic solvents such as CH2Cl2 and CHCl3. 相似文献
49.
50.