全文获取类型
收费全文 | 10215篇 |
免费 | 1710篇 |
国内免费 | 494篇 |
专业分类
化学 | 4471篇 |
晶体学 | 38篇 |
力学 | 1330篇 |
综合类 | 239篇 |
数学 | 2593篇 |
物理学 | 3748篇 |
出版年
2025年 | 10篇 |
2024年 | 182篇 |
2023年 | 179篇 |
2022年 | 438篇 |
2021年 | 457篇 |
2020年 | 523篇 |
2019年 | 393篇 |
2018年 | 334篇 |
2017年 | 461篇 |
2016年 | 514篇 |
2015年 | 442篇 |
2014年 | 584篇 |
2013年 | 618篇 |
2012年 | 670篇 |
2011年 | 575篇 |
2010年 | 487篇 |
2009年 | 568篇 |
2008年 | 551篇 |
2007年 | 543篇 |
2006年 | 514篇 |
2005年 | 454篇 |
2004年 | 412篇 |
2003年 | 349篇 |
2002年 | 300篇 |
2001年 | 260篇 |
2000年 | 248篇 |
1999年 | 198篇 |
1998年 | 204篇 |
1997年 | 161篇 |
1996年 | 132篇 |
1995年 | 129篇 |
1994年 | 98篇 |
1993年 | 84篇 |
1992年 | 70篇 |
1991年 | 40篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 19篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 29篇 |
1984年 | 19篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 15篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
《Discrete Mathematics》2022,345(11):112983
We determine the 22 isomorphism classes of 4-GDDs with group type and compare their automorphism groups. We also observe for the first time an example of a three dimensional Pasch triangle in a GDD. 相似文献
3.
Karolina Graczyk Tobias Haven Prof. Dr. Lutz Ackermann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(24):8812-8815
The so‐called magic methyl effect significantly boosts the bioactivities and physical properties of pharmacologically active drugs. Direct introduction of the methyl group by C?H activation was accomplished with a versatile iron catalyst, which enabled the C?H methylation of (hetero)benzamides, anilides, alkenes, and even alkanes by triazole assistance in a chemo‐, site‐ and diastereo‐selective fashion. 相似文献
4.
Light‐Controlled Histone Deacetylase (HDAC) Inhibitors: Towards Photopharmacological Chemotherapy
下载免费PDF全文

Dr. Wiktor Szymanski Maria E. Ourailidou Dr. Willem A. Velema Prof. Dr. Frank J. Dekker Prof. Dr. Ben L. Feringa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(46):16517-16524
Cancer treatment suffers from limitations that have a major impact on the patient’s quality of life and survival. In the case of chemotherapy, the systemic distribution of cytotoxic drugs reduces their efficacy and causes severe side effects due to nonselective toxicity. Photopharmacology allows a novel approach to address these problems because it employs external, local activation of chemotherapeutic agents by using light. The development of photoswitchable histone deacetylase (HDAC) inhibitors as potential antitumor agents is reported herein. Analogues of the clinically used chemotherapeutic agents vorinostat, panobinostat, and belinostat were designed with a photoswitchable azobenzene moiety incorporated into their structure. The most promising compound exhibits high inhibitory potency in the thermodynamically less stable cis form and a significantly lower activity for the trans form, both in terms of HDAC activity and proliferation of HeLa cells. This approach offers a clear prospect towards local photoactivation of HDAC inhibition to avoid severe side effects in chemotherapy. 相似文献
5.
In-tube magnetic solid phase microextraction (in-tube MSPME) of fluoroquinolones from water and urine samples based on the use of sodium dodecyl sulfate (SDS) coated Fe3O4 nanoparticles packed tube has been reported. After the preparation of Fe3O4 nanoparticles (NPs) by a batch synthesis, these NPs were introduced into a stainless steel tube by a syringe and then a strong magnet was placed around the tube, so that the Fe3O4 NPs were remained in the tube and the tube was used in the in-tube SPME-HPLC/UV for the analysis of fluoroquinolones in water and urine samples. Plackett–Burman design was employed for screening the variables significantly affecting the extraction efficiency. Then, the significant factors were more investigated by Box–Behnken design. Calibration curves were linear (R2 > 0.990) in the range of 0.1–1000 μg L−1 for ciprofloxacin (CIP) and 0.5–500 μg L−1 for enrofloxacin (ENR) and ofloxacin (OFL), respectively. LODs for all studied fluoroquinolones ranged from 0.01 to 0.05 μg L−1. The main advantages of this method were rapid and easy automation and analysis, short extraction time, high sensitivity, possibility of fully sorbent collection after analysis, wide linear range and no need to organic solvents in extraction. 相似文献
6.
7.
Abdurrahman Turksoy Samir Bouayad-Gervais Prof. Franziska Schoenebeck 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(46):e202201435
While the N-trifluoromethylation of cyclic ureas is of interest for the potential to fundamentally change the properties of these biologically relevant moieties, the single synthetic procedure known to date describing their access only gives 4,4-disubstituted or fused aromatic cyclic N-CF3 urea derivatives. We herein report an alternative approach to unleash access to the 4-monosubstituted imidazolidinone motif. The strategy relies on straightforward cyclization of readily accessible acyclic ureas, enabled by Ag-catalysis or light-assisted proton coupled electron transfer. The cyclic core is shown to be highly robust and amenable to various derivatizations, such as tandem Ni-catalysis, C−B, C−N, C−C cross couplings or C−H functionalizations, tolerating basic, nucleophilic and/or oxidizing conditions. 相似文献
8.
Based on the dual theory of nonlinear mathematical programming and the second order Taylor series expansions of functions,
an efficient algorithm for structural optimum design has been developed. The main advantages of this method are the generality
in use, the efficiency in computation and the capability in identifying automatically the set of active constraints. On the
basis of the virtual work principle, formulas in terms of element stresses for the first and second order derivatives of nodal
displacement and stress with respect to design variables are derived. By applying the Saint-Venant's principle, the computational
efforts involved in the Hessian matrix associated with the iterative expression can be significantly reduced. This method
is especially suitable for optimum design of large scale structures. Several typical examples have been optimized to test
its uasefulness. 相似文献
9.
电除尘器本体结构优化设计是一个规模大,设计变量数多而具有相当难度的几何可调和拓扑可调优化设计问题。对这样一个大型复杂的结构优化问题,本文在文[1]的工作基础上,充分利用结构的力学特性,应用有效设计变量的概念,建立了不用求偏导数且不必解线性规划的可行方向法—KFD方法。该方法具有收敛速度快、占用内存少的优点,比通常ε有效约束可行方向法提高速度数十倍。实际应用的结果表明文中的方法是很有效的。 相似文献
10.
非高斯随机激励下工程结构可靠性估计的一种方法 总被引:1,自引:0,他引:1
本文将工程结构考虑为振动系统,把随机载荷及在结构上的载荷效应作为随机过程,分析状态函数的高阶矩,进行最大熵概率分析,得到结构在随机载荷作用下失效的概率。此法为随机环境下工作的结构、构件或设备的安全设计、可靠性检验提供了一个可行的方法。 相似文献