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   115231篇
  免费   17235篇
  国内免费   12235篇
化学   61450篇
晶体学   807篇
力学   5670篇
综合类   470篇
数学   10056篇
物理学   34612篇
无线电   31636篇
  2024年   510篇
  2023年   2879篇
  2022年   3614篇
  2021年   4689篇
  2020年   4541篇
  2019年   4190篇
  2018年   3650篇
  2017年   3489篇
  2016年   4965篇
  2015年   5295篇
  2014年   6267篇
  2013年   7926篇
  2012年   9745篇
  2011年   9791篇
  2010年   7037篇
  2009年   6872篇
  2008年   7314篇
  2007年   6571篇
  2006年   6125篇
  2005年   5196篇
  2004年   3826篇
  2003年   3353篇
  2002年   3066篇
  2001年   2584篇
  2000年   2427篇
  1999年   2633篇
  1998年   2225篇
  1997年   2011篇
  1996年   1994篇
  1995年   1687篇
  1994年   1474篇
  1993年   1205篇
  1992年   1076篇
  1991年   899篇
  1990年   748篇
  1989年   529篇
  1988年   444篇
  1987年   355篇
  1986年   305篇
  1985年   277篇
  1984年   191篇
  1983年   139篇
  1982年   111篇
  1981年   85篇
  1980年   80篇
  1979年   43篇
  1978年   35篇
  1977年   46篇
  1976年   39篇
  1973年   29篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Low-grade heat energy recycling is the key technology of waste-heat utilization, which needs to be improved. Here, we use a zinc-assisted solid-state pyrolysis route to prepare zinc-guided 3D graphene (ZnG), a 3D porous graphene with the interconnected structure. The obtained ZnG, with a high specific surface area of 1817 m2·g−1 and abundant micropores and mesopores, gives a specific capacitance of 139 F·g−1 in a neutral electrolyte when used as electrode material for supercapacitors. At a high current density of 8 A·g−1, the capacitance retention is 93% after 10,000 cycles. When ZnG is used for thermally chargeable supercapacitors, the thermoelectric conversion of the low-grade heat energy is successfully realized. This work thus provides a demonstration for low-grade heat energy conversion.  相似文献   
992.
In the domain of network science, the future link between nodes is a significant problem in social network analysis. Recently, temporal network link prediction has attracted many researchers due to its valuable real-world applications. However, the methods based on network structure similarity are generally limited to static networks, and the methods based on deep neural networks often have high computational costs. This paper fully mines the network structure information and time-domain attenuation information, and proposes a novel temporal link prediction method. Firstly, the network collective influence (CI) method is used to calculate the weights of nodes and edges. Then, the graph is divided into several community subgraphs by removing the weak link. Moreover, the biased random walk method is proposed, and the embedded representation vector is obtained by the modified Skip-gram model. Finally, this paper proposes a novel temporal link prediction method named TLP-CCC, which integrates collective influence, the community walk features, and the centrality features. Experimental results on nine real dynamic network data sets show that the proposed method performs better for area under curve (AUC) evaluation compared with the classical link prediction methods.  相似文献   
993.
Stereoselective isomerization of α-alkyl styrenes is accomplished using a new iron catalyst supported by phosphine-pyridine-oxazoline (PPO) ligand.The protocol ...  相似文献   
994.
认股权证的等价鞅测度定价模型与数值方法   总被引:13,自引:0,他引:13  
刘志强  金朝蒿 《经济数学》2004,21(2):136-140
本文对认股权证应用等价鞅测度方法进行定价 .推导出计算更自然、更简单的类似 Black- Scholes模型的认股权证定价公式 .给出了一种比较好的数值计算方法 .并讨论了认股权证在中国证券市场的发展状况 .  相似文献   
995.
从Bα到Qk的复合算子   总被引:1,自引:0,他引:1  
张芳  刘永民  王峰 《数学研究》2007,40(4):374-381
用K—Carleson测度刻画了B^α(B0^α)到QK的复合算子的有界性,以及B^α到QK,0的复合算子的有界性和紧性.  相似文献   
996.
1IntroductionIn[1]theexistence0fweaksoluti0ns0fdegeneratequasilinearparabolicinitialboundaryvaluepr0blemonthespaceXT=Lp(O,T;V)hasbeenpr0ved,whereQT=(O,T)xfl,V=W:"(v,fl),whichisaweightedS0b0levspace.Thedegenerati0nisdeterminedbyavectorfunctionv(x)=(v.(x)),IaI=m,withp0sitivec0mponentsv.(x)inflsatisfyingcertainintegrabilityassumptions.Theaim0fthispaperistosh0wsomeattractivitypr0perties0ftheso1ution(ast-oo).Similarresultsf0rparab0licequati0nscanbefounde-g.in[2],[3].Letflbeab0unded0pensubset…  相似文献   
997.
1+1维经典可积系统的隐代数结构用Riemann-Hilbert变换进行一般性讨论。新的Loop代数用Yang-Baxter等式的解给出,并指出它与基本Poisson-Lie括号的一致性。系统的Virasoro代数结构由系统的共形不变性导出。  相似文献   
998.
Cancer is one of the most difficult diseases in human society. Therefore, it is urgent for us to understand its pathogenesis and improve the cure rate. Exosomes are nanoscale membrane vesicles formed by a variety of cells through endocytosis. As a new means of intercellular information exchange, exosomes have attracted much attention. Noncoding RNAs exist in various cell compartments and participate in a variety of cellular reactions; in particular, they can be detected in exosomes bound to lipoproteins and free circulating molecules. Increasing evidence has suggested the potential roles of exosomal noncoding RNAs in the progression of tumors. Herein, we present a comprehensive update on the biological functions of exosomal noncoding RNAs in the development of cancer. Specifically, we mainly focus on the effects of exosomal noncoding RNAs, including microRNAs, circular RNAs, long noncoding RNAs, small nuclear RNAs, and small nucleolar RNAs, on tumor growth, metastasis, angiogenesis, and chemoresistance. Moreover, we outline the current clinical implications concerning exosomal noncoding RNAs in cancer treatment.Subject terms: Cancer, Non-coding RNAs  相似文献   
999.
This paper studies the effects of hygrothermal environment at different tempera-tures and ultraviolet(UV)radiation on the bending properties of epoxy polymer mo...  相似文献   
1000.
On a lattice with 2+1-flavor dynamical domain-wall fermions at the physical pion mass,we calculate the decay constants of D_s* , D* ,and φ .The lattice size is 48^3×96 ,which corresponds to a spatial extension of -5.5 fm,with a lattice spacing of a\approx a≈0.114 fm.For the valence light,strange,and charm quarks,we use overlap fermions at several mass points close to their physical values.Our results at the physical point are fD=213(5) MeV, fDs=249(7) MeV, fD*=234(6) MeV, fDs*=274(7) MeV,and fDs=241(9) MeV.The couplings of D* and D_s* to the tensor current( fVT )can be derived from ratios fD*^T/fD*=0.91(4) and fDs*^T/fDs*=0.92(4) ,respectively,which are the first lattice quantum chromodynamics(QCD)results.We also obtain ratios fD*/fD=1.10(3) and fDs*/fDs=1.10(4) ,which reflect the size of heavy quark symmetry breaking in charmed mesons.Ratios fDs/fD=1.16(3) and fDs*/fD*=1.17(3) can be taken as a measure of SU(3)flavor symmetry breaking.  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