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   20665篇
  免费   1398篇
  国内免费   2914篇
化学   16145篇
晶体学   134篇
力学   708篇
综合类   177篇
数学   4818篇
物理学   2995篇
  2024年   41篇
  2023年   339篇
  2022年   1292篇
  2021年   1099篇
  2020年   1075篇
  2019年   892篇
  2018年   842篇
  2017年   857篇
  2016年   953篇
  2015年   853篇
  2014年   1058篇
  2013年   2198篇
  2012年   1349篇
  2011年   1179篇
  2010年   858篇
  2009年   1253篇
  2008年   1239篇
  2007年   1078篇
  2006年   881篇
  2005年   806篇
  2004年   651篇
  2003年   505篇
  2002年   658篇
  2001年   296篇
  2000年   346篇
  1999年   343篇
  1998年   285篇
  1997年   248篇
  1996年   229篇
  1995年   186篇
  1994年   162篇
  1993年   129篇
  1992年   108篇
  1991年   87篇
  1990年   53篇
  1989年   83篇
  1988年   56篇
  1987年   32篇
  1986年   33篇
  1985年   57篇
  1984年   67篇
  1983年   30篇
  1982年   42篇
  1981年   31篇
  1980年   25篇
  1979年   24篇
  1978年   17篇
  1977年   10篇
  1976年   13篇
  1973年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Catalytic decomposition of NO over Cu-Os/13X has been carried out in a tubular fixed bed reactor at atmospheric pressure and the results were compared with literature data performed by high-throughput screening (HTS). The activity and durability of Cu-Os/13X prepared by conventional ion-exchange method have been investigated in the presence of H2O and SO2. It was found that Cu-Os/13X prepared by ion-exchange shows a high activity in a wide temperature range in selective catalytic reduction (SCR) of NO with C3H6 compared to Cu/13X, proving the existence of more NO adsorption site on Cu-Os/13X. However, Cu-Os/13X exhibited low activity in the presence of water, and was quite different from the result reported in literature. SO2 resistance is also low and does not recover its original activity when the SO2 was blocked in the feed gas stream. This result suggested that catalytic activity between combinatorial screening and conventional testing should be compared to confirm the validity of high-throughput screening.  相似文献   
52.
The characteristic exponent α of a Lévy-stable law S α (σ, β, μ) was thoroughly studied as the extreme value index of a heavy tailed distribution. For 1 < α < 2, Peng (Statist. Probab. Lett. 52: 255–264, 2001) has proposed, via the extreme value approach, an asymptotically normal estimator for the location parameter μ. In this paper, we derive by the same approach, an estimator for the scale parameter σ and we discuss its limiting behavior.   相似文献   
53.
Let T be a bounded linear operator in a Banach space, with σ(T)={1}. In 1983, Esterle-Berkani' s conjecture was proposed for the decay of differences (I - T) T^n as follows: Eitheror lim inf (n→∞(n+1)||(I-T)T^n||≥1/e or T = I. We prove this claim and discuss some of its consequences.  相似文献   
54.
可允许集上的广义向量拟均衡问题   总被引:2,自引:0,他引:2  
主要讨论可允许集上的广义向量拟均衡问题,推广L in的一些结果.  相似文献   
55.
牛顿弦截法预估校正迭代格式的收敛阶   总被引:2,自引:0,他引:2  
研究如下形式的牛顿弦截法的预估校正(P.C.)格式:P(预估):~xk+1=xk-(xk-xk-1)f(xk)f(xk)-f(xk-1)C(校正):xk+1=xk-(~xk+1-xk)f(xk)f~(xk+1)-f(xk)证明了它的收敛阶为2.618.  相似文献   
56.
Utilization of carbohydrates by radiation processing   总被引:2,自引:0,他引:2  
Upgrading and utilization of carbohydrates such as chitosan, sodium alginate, carrageenan, cellulose, pectin have been investigated for recycling these bio-resources and reducing the environmental pollution. These carbohydrates were easily degraded by irradiation and various kinds of biological activities such as anti-microbial activity, promotion of plant growth, suppression of heavy metal stress, phytoalexins induction, etc. were induced. On the other hand, some carbohydrate derivatives, carboxymethylcellulose and carboxymethylstarch, could be crosslinked under certain radiation condition and produce the biodegradable hydrogel for medical and agricultural use.  相似文献   
57.
Vertex-reinforced random walk is a random process which visits a site with probability proportional to the weight w k of the number k of previous visits. We show that if w k k α, then there is a large time T 0 such that after T 0 the walk visits 2, 5, or ∞ sites when α < 1, = 1, or > 1, respectively. More general results are also proven.   相似文献   
58.
The Fe73.5Cu1Nb3Si13.5B9 FINEMET alloy has been prepared by the rapid solidification technique. The critical behaviour of this alloy in the amorphous as well as in its nanocrystalline states has been studied near their respective Curie temperatures. From the values of the critical exponents one can conclude that the alloy behaves like a 3D Heisenberg ferromagnet in the amorphous and nanocrystalline states. But there exists a slight increase in the value of β for the alloy annealed at 823 K (the nanocrystalline state) as observed in most of the amorphous alloys.  相似文献   
59.
The phase boundary theory and the contact rule of phase regions are compared, and some weaknesses of the latter are manifested. The comparison between the Gupta’s method and the boundary theory method for constructing multicomponent isobaric sections is also presented.  相似文献   
60.
Let μ+(t) and μ(t) be the locations of the maximum and minimum, respectively, of a standard Brownian motion in the interval [0,t]. We establish a joint integral test for the lower functions of μ+(t) and μ(t), in the sense of Paul Lévy. In particular, it yields the law of the iterated logarithm for max(μ+(t),μ(t)) as a straightforward consequence. Our result is in agreement with well-known theorems of Chung and Erdős [(1952) Trans. Amer. Math. Soc. 72, 179–186.], and Csáki, F?ldes and Révész [(1987) Prob. Theory Relat. Fields 76, 477–497].   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