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   7718篇
  免费   1181篇
  国内免费   1037篇
化学   5721篇
晶体学   48篇
力学   483篇
综合类   68篇
数学   864篇
物理学   2752篇
  2024年   6篇
  2023年   144篇
  2022年   149篇
  2021年   251篇
  2020年   331篇
  2019年   311篇
  2018年   224篇
  2017年   202篇
  2016年   323篇
  2015年   355篇
  2014年   384篇
  2013年   510篇
  2012年   623篇
  2011年   708篇
  2010年   457篇
  2009年   444篇
  2008年   513篇
  2007年   442篇
  2006年   444篇
  2005年   424篇
  2004年   297篇
  2003年   259篇
  2002年   262篇
  2001年   235篇
  2000年   174篇
  1999年   166篇
  1998年   159篇
  1997年   143篇
  1996年   139篇
  1995年   156篇
  1994年   118篇
  1993年   113篇
  1992年   74篇
  1991年   98篇
  1990年   66篇
  1989年   67篇
  1988年   48篇
  1987年   33篇
  1986年   23篇
  1985年   17篇
  1984年   12篇
  1983年   11篇
  1982年   11篇
  1981年   5篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
  1966年   1篇
  1957年   1篇
排序方式: 共有9936条查询结果,搜索用时 203 毫秒
41.
The Hawking radiation of Dirac particles in an arbitrarily rectilinearly accelerating Kinnersley black hole with electromagnetic charge and cosmological constant is investigated by using the generalized tortoise coordinate transformation. Both the location and the temperature of the event horizon depend on the time and the polar angle. The Hawking thermal radiation spectrum of Dirac particles is also derived.  相似文献   
42.
采用酶联反应荧光法测定样品中烯醇化酶的总活性。方法最低检出限为02IU/L,在020~35IU/L范围标准曲线呈线性,γ>0997,回收率达90%,相对标准偏差<10%。对临床确诊的视网膜母细胞瘤进行了初步探讨,检验结果的特异性较高。  相似文献   
43.
The author gives an optimum estimate of the first eigenvalue of a compact Riemannian manifold. It is shown that let M be a compact Riemannian manifold, then the first eigenvalue λ_1 of the Laplace operator of M satisfies α_1+max{0,-(n-1)K}≥π~2/d~2 where d is the diameter of M and (n-1)K is the negative lower bound of the Ricci curvature of M.  相似文献   
44.
In this article we survey the Trefftz method (TM), the collocation method (CM), and the collocation Trefftz method (CTM). We also review the coupling techniques for the interzonal conditions, which include the indirect Trefftz method, the original Trefftz method, the penalty plus hybrid Trefftz method, and the direct Trefftz method. Other boundary methods are also briefly described. Key issues in these algorithms, including the error analysis, are addressed. New numerical results are reported. Comparisons among TMs and other numerical methods are made. It is concluded that the CTM is the simplest algorithm and provides the most accurate solution with the best numerical stability. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007  相似文献   
45.
热等离子体裂解天然气制备C2烃   总被引:1,自引:0,他引:1  
采用氮气热等离子体来裂解天然气制备乙炔乙烯,着重研究了天然气转化率和乙炔、乙烯收率随氮气流量和天然气流量的变化.结果表明,天然气流量与氮气流量之比为11时,可得到较好的结果.当等离子体功率为15kW、天然气流量为3Nm3*h-1、氮气流量为3Nm3*h-1时得到最好的结果.这时天然气转化率为57%,乙炔、乙烯的收率分别为34%和9%;乙炔在反应气中的体积浓度为7.5%,与部分氧化法相似;扣除不参加反应的氮气,乙炔在气相产品中的体积浓度为13.2%,与热力学平衡计算结果基本符合.  相似文献   
46.
The following results are proved in this paper. Let G be a 2k-edge-connected eulerian graph. (i) For every set {e1, e2, ?, e2k+1} ? E(G) there is an eulerian trail T of the form e1, e2, ?, e2k+1, ?. (ii) For every set E* = {e1, e2, ?, ek} ? E(G) there is an eulerian trail T = e1, ?, e2, ?, ek, ? in which the elements of E* are traversed in accordance with a prescribed orientation. © 1995 John Wiley & Sons, Inc.  相似文献   
47.
In this paper, continuous wave Yb3+-doped double-clad fiber lasers (DCFLs) with linear-cavity are investigated theoretically and numerically using the rate equations. Under the steady state conditions, the simplified analytic solutions of Yb3+-doped DCFLs under considering the scattering loss are deduced in the strongly pump condition. Compared with the known analytic solutions in published literatures, our analytic solutions are more accurate, especially, at higher reflectivity of output mirror. In addition, a fast and stable algorithm based on the Newton-Raphson method is proposed to simulate numerically Yb3+-doped DCFLs. The results by simplified analytic solutions are in good agreement with those by the numerical simulation. Moreover, we have performed the optimization of an Yb3+-doped DCFL using the simplified analytic solutions and the numerical simulations, respectively.  相似文献   
48.
用锌有机源和CO2/H2混合气源PECVD沉积ZnO薄膜   总被引:2,自引:0,他引:2  
在等离子体作用下,以CO2/H2混合气为氧源,Zn(C2H5)2锌为锌源,在单晶硅上生长出高度择优取向的氧化锌薄膜。X射线衍射分析表明,薄膜为六方结构,c轴高度择优;原子力显微镜观察到晶粒是有规律地按六方排布,薄膜的表面粗糙度较小;从光致发光谱还发现在380 nm处有非常强的紫外峰。  相似文献   
49.
The second law of thermodynamics is one of the most fundamental and for-reaching laws of physics. It teaches us that when a closed system undergoes a thermodynamic process the entropy of the system never decreases; it increases, or at least remains constant. If the entropy increases the thermodynamic process is irreversible, otherwise it is reversible. Only ideal thermal process is reversible. In classical world a great number of facts have proved the second law is true. But in quantum world since the quantum coherence and correlations exist we are not sure the second law is still true, at least in principle. This is because that: 1. on the microscopic level the irreversibility is conflict with the reversibility of all fundamental physical laws ; 2. there are not enough evidences to show it is true in quantum world.  相似文献   
50.
The melting curve of MgSiO分子动力学 MgSiO3钙钛矿 熔化温度 高压melting temperature, molecular dynamics, high pressureProject supported by the National Natural Science Foundation of China (Grant Nos 10274055 and 10376021),the Natural Science Foundation of Gansu Province, China (Grant No 3ZS051-A25-027) and the Scientific Research Foundation of Education Bureau of Gansu Province, China (Grant No 0410-01).2005-01-125/8/2005 12:00:00 AMThe melting curve of MgSiO3 perovskite is simulated using molecular dynamics simulations method at high pressure. It is shown that the simulated equation of state of MgSiO3 perovskite is very successful in reproducing accurately the experimental data. The pressure dependence of the simulated melting temperature of MgSiO3 perovskite reproduces the stability of the orthorhombic perovskite phase up to high pressure of 130GPa at ambient temperature, consistent with the theoretical data of the other calculations. It is shown that its transformation to the cubic phase and melting at high pressure and high temperature are in agreement with recent experiments.  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