首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4384篇
  免费   575篇
  国内免费   896篇
化学   2001篇
晶体学   75篇
力学   92篇
综合类   42篇
数学   226篇
物理学   883篇
综合类   2536篇
  2024年   13篇
  2023年   51篇
  2022年   80篇
  2021年   115篇
  2020年   113篇
  2019年   100篇
  2018年   103篇
  2017年   128篇
  2016年   137篇
  2015年   174篇
  2014年   219篇
  2013年   251篇
  2012年   288篇
  2011年   307篇
  2010年   337篇
  2009年   348篇
  2008年   381篇
  2007年   366篇
  2006年   389篇
  2005年   308篇
  2004年   245篇
  2003年   204篇
  2002年   231篇
  2001年   230篇
  2000年   216篇
  1999年   119篇
  1998年   63篇
  1997年   33篇
  1996年   39篇
  1995年   31篇
  1994年   38篇
  1993年   24篇
  1992年   28篇
  1991年   26篇
  1990年   18篇
  1989年   17篇
  1988年   20篇
  1987年   11篇
  1986年   9篇
  1985年   11篇
  1984年   7篇
  1983年   9篇
  1982年   4篇
  1981年   3篇
  1979年   4篇
  1966年   1篇
  1963年   1篇
  1959年   1篇
  1957年   1篇
  1955年   3篇
排序方式: 共有5855条查询结果,搜索用时 15 毫秒
691.
Genetically modified (GM) livestock have the potential to contribute to improving the environment and human health, with consumption of fewer resources and reduced waste production. However, the transgene process also poses risks. The safety assessment and control of transgenic animal products have drawn wide attention, and the relevant regulations and technology are being developed. Quick testing technology plays a significant role in on-site and customs sampling. Nowadays, loop-mediated isothermal amplification (LAMP) was widely applied in nucleic acid analysis because of its simplicity, rapidity, high efficiency and specificity. In this study, a specific, sensitive detection system for detecting sFAT-1 transgenic pigs was designed. A set of six primers including two loop primers was designed for the target sequence. The DNA samples were amplified in less than 1 h at the optimized temperature and detecting by both Nephelometer LA-320c and unaided eyes directly adding calcein. The detection limit of sFAT-1 LAMP was as low as 1.26 ng/μL. Furthermore, blind tests of transgenic and non-transgenic DNA samples were all correctly detected. Hence, the results in this study demonstrated that LAMP is a very useful tool for transgenic detection.  相似文献   
692.
It has been proved that the vanishing of Tate homology is a sufficient condition for the derived depth formula to hold in [J. Pure Appl. Algebra, 219, 464–481(2015)]. In this paper, we investigate when Tate homology vanishes by studying the stable homology theory for complexes. Properties such as the balancedness and vanishing of stable homology for complexes are studied. Our results show that the vanishing of this homology can detect finiteness of homological dimensions of complexes and regularness of rings.  相似文献   
693.
Let C be a triangulated category with a proper class E of triangles.We prove that there exists an Avramov–Martsinkovsky type exact sequence in C,which connects E-cohomology,E-Tate cohomology and E-Gorenstein cohomology.  相似文献   
694.
利用Matlab语言将EFIT程序反演计算过程进行优化整合,简化了程序操作步骤,并增加了对计算结果的分析与存储功能。利用整合后的 EFIT 程序,计算分析了 J-TXET 装置放电过程中等离子体磁场位形和其它参数的演变,绘制了等离子体压强剖面图、等离子体电流密度和安全因子分布等磁面信息的重建结果。此外,还将反演结果与软X射线测算数据进行比对。结果表明,改善后的EFIT程序能够初步满足对实验放电的反演计算分析要求,为J-TXET装置的放电控制和运行提供重要的参考数据。  相似文献   
695.
Mononuclear copper(II) and trinuclear cobalt(II) complexes, namely [Cu(L1)]2 · CH2Cl2 and [{Co(L2)(EtOH)}2Co(H2O)] · EtOH {H2L1 = 4,6‐dichloro‐6′‐methyoxy‐2,2′‐[1,1′‐(ethylenedioxydinitrilo)dimethylidyne]diphenol and H3L2 = 6‐ethyoxy‐6′‐hydroxy‐2,2′‐[1,1′‐(ethylenedioxydinitrilo)dimethylidyne]diphenol}, were synthesized and characterized by elemental analyses, IR and UV/Vis spectroscopy, and single‐crystal X‐ray diffraction. In the CuII complex, the CuII atom is four‐coordinate, with a N2O2 coordination sphere, and has a slightly distorted square‐planar arrangement. Interestingly, the obtained trinuclear CoII complex is different from the common reported 2:3 (L:CoII) salamo‐type CoII complexes. Infinite 2D layer supramolecular structures are formed via abundant intermolecular hydrogen bonding and π ··· π stacking interactions in the CuII and CoII complexes.  相似文献   
696.
MGMT protein, which has been associated with resistance to antitumor alkylation drugs for many patients, is a very useful prognostic marker to provide a guide for therapeutic decisions. Considering the large number of cellular samples that have to be handled daily at the hospitals, it is thus important to develop a rapid and simple analytical method to distinguish MGMT activity in different types of cells. In this paper, we describe a MGMT‐activated fluorescence turn‐on probe for the rapid no‐wash imaging of MGMT in living cells. The probe consists of a specific MGMT suicide pseudosubstrate, O6‐benzyl‐guanine and an environment‐sensitive fluorophore, SBD. In the presence of MGMT, the enzyme transfers SBD to the protein active site where the hydrophobic surrounding causes the fluorophore to exhibit more than 50‐fold fluorescence enhancement. With this probe, bright fluorescence was observed for MGMT‐positive, Hela S3 and MCF‐7 cells, while MGMT‐deficient CHO cells displayed no fluorescence. We believe that this fluorescence activation probe design can also be extended to detect other transferases, for which there are still no effective methods to image them in living cells.  相似文献   
697.
We theoretically investigate the electricity storage/generation in a reversible solid oxide cell stack. The system heat is for the first time tentatively stored in a phase-change metal when the stack is operated to generate electricity in a fuel cell mode and then reused to store electricity in an electrolysis mode. The state of charge (H2 frication in cathode) effectively enhances the open circuit voltages (OCVs) while the system gas pressure in electrodes also increases the OCVs. On the other hand, a higher system pressure facilitates the species diffusion in electrodes that therefore accordingly improve electrode polarizations. With the aid of recycled system heat, the roundtrip efficiency reaches as high as 92% for the repeated electricity storage and generation.  相似文献   
698.
In this study, we synthesized molybdenum disulfide/polyaniline (MoS2/PANI) nanocomposite via in situ polymerization of aniline in the presence of thin-layered MoS2. The as-prepared MoS2/PANI nanocomposite obtained an improved electrochemical performance due to the physisorption interaction between aromatic aniline and the basal plane of MoS2. Furthermore, we constructed a new kind of electrochemical sensor based on MoS2/PANI nanocomposite for the detection of chloramphenicol, which showed an excellent performance. The sensor has a high sensitivity and wide detection range from 1×10-7 mol/L to 1×10-4 mol/L, with a low detection limit of 6.9×10-8 mol/L.  相似文献   
699.
庄乾乾  程希骏  李静 《数学杂志》2016,36(4):841-850
本文研究了期货期权和裂解价差期权的定价问题.利用Fourier变换方法,在ASub CIR模型的基础上,获得了单因素期货期权,两因素期货期权以及价差期权价格的表达式,最后用C++和MATLAB计算出期权的价格,解决了利用特征函数展开法计算期权价格时速度较慢且不稳定的问题.  相似文献   
700.
A new method for the synthesis of di‐ and trisubstituted pyrroles via copper‐catalyzed cyclization of ethyl allenoates with activated isocyanides has been developed. In contrast to related annulation reactions previously reported, this new process features a skeletal rearrangement in which the aryl sulfonyl moiety, which functions as the electron‐withdrawing group in the α‐carbon of the isocyanide, was found to migrate to the γ‐carbon of the starting allenoate in the final product for the first time.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号