全文获取类型
收费全文 | 46357篇 |
免费 | 5855篇 |
国内免费 | 5901篇 |
专业分类
化学 | 34388篇 |
晶体学 | 638篇 |
力学 | 2168篇 |
综合类 | 491篇 |
数学 | 5466篇 |
物理学 | 14962篇 |
出版年
2024年 | 109篇 |
2023年 | 616篇 |
2022年 | 1192篇 |
2021年 | 1302篇 |
2020年 | 1378篇 |
2019年 | 1449篇 |
2018年 | 1237篇 |
2017年 | 1166篇 |
2016年 | 1809篇 |
2015年 | 1893篇 |
2014年 | 2262篇 |
2013年 | 3175篇 |
2012年 | 3680篇 |
2011年 | 3941篇 |
2010年 | 2857篇 |
2009年 | 2789篇 |
2008年 | 3254篇 |
2007年 | 2973篇 |
2006年 | 2713篇 |
2005年 | 2322篇 |
2004年 | 1979篇 |
2003年 | 1699篇 |
2002年 | 1758篇 |
2001年 | 1449篇 |
2000年 | 1172篇 |
1999年 | 1013篇 |
1998年 | 775篇 |
1997年 | 715篇 |
1996年 | 695篇 |
1995年 | 590篇 |
1994年 | 548篇 |
1993年 | 509篇 |
1992年 | 478篇 |
1991年 | 388篇 |
1990年 | 335篇 |
1989年 | 274篇 |
1988年 | 215篇 |
1987年 | 181篇 |
1986年 | 179篇 |
1985年 | 190篇 |
1984年 | 126篇 |
1983年 | 82篇 |
1982年 | 83篇 |
1981年 | 66篇 |
1980年 | 62篇 |
1979年 | 61篇 |
1978年 | 51篇 |
1976年 | 44篇 |
1974年 | 45篇 |
1973年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
PURE STATE APPROACH TO C(x)_αZ_nLIBINGREN;LINQING(InstituteofMathematics,AcademiaSinica,Beijing100080,China.Projectsupportedbyth?.. 相似文献
82.
A novel heath monitoring system of the rocket based on fiber optic Bragg gratings is brought forward, its component units and working principle are also described. 相似文献
83.
By introducing an imaginary space transform curvature ρs, a complex space called Riemannian space is constructed, in which the light propagating in free space has the trajectory
of straight line while propagating. Moreover, this curvature couples with that of the wave front of the paraxial beam ρw, and therefore a complex curvature ρc is constructed, which can be employed to investigate the behavior of the light transmission and to generalize the ABCD law.
Project supported by the National Hi-Tech Inertial Confinement Fusion Committee, the Guangdong Natural Science Foundation
the Postdoctoral Foundation of Guangdong and National Postdoctoral Foundation of China. 相似文献
84.
用传统的预测效度估计法估计高考预测效度,其估计值往往偏低。为此,本文应用回归分析中混合估计理论提出了高考预测效度的混合估计。这种估计是预测效度的无偏估计,并解决了预测效度估计值偏低的问题。 相似文献
85.
Ga1-xInxAs(x>0.53)材料是未来长距离低损耗光纤通信的理想光源材料和探测器材料之一.我们采用水平常压MOCVD系统,在InP衬底上成功地生长了Ga1-xInxAs(x>0.53)/InAsyP1-y/Inp异质结材料.其中InAs1-yPy为组份阶梯变化的多层结构.由样品的(400)面X光衍射结果测定了各层组份.由二次离子质谱(SIMS)得到了样品剖面组份变化结果,证明InAs1-yPy层组份为阶梯状变化的.通过对光致发光结果和X光衍射结果比较,可以看到,InAsyP1-y层通过位错和弹性畸变二种方式来释放或积累Ga1-xInxAs与InP间的失配应力,从而减少了Ga1-xInxAs中的失配位错.有效地改善了Ga1-xInxAs的质量.已获得了x高达0.94表面光亮的Ga1-xInxAs/InAs1-yPy/InP异质结材料. 相似文献
86.
Lin Zhengyan 《数学年刊B辑(英文版)》1998,19(3):281-292
§1.IntroductionandResultsLet{Xn,n1}beasequenceofrandomvariableswithacommondistributionfunctionF(x)andletXn1Xn2…Xnnbetheor... 相似文献
87.
LetK be a compact Hausdorff space, and letT be an irreducible Markov operator onC(K). We show that ifgεC(K) satisfies sup
N
‖Σ
j
=0N
T
j
g‖<∞, then (and only then) there existsfεC(K) with (I − T)f=g. Generalizing the result to irreducible Markov operator representations of certain semi-groups, we obtain that bounded cocycles
are (continuous) coboundaries. For minimal semi-group actions inC(K), no restriction on the semi-group is needed. 相似文献
88.
Hong Wang 《Graphs and Combinatorics》1994,10(2-4):271-281
Letk and s be two positive integers with s≥3. LetG be a graph of ordern ≥sk. Writen =qk + r, 0 ≤r ≤k - 1. Suppose thatG has minimum degree at least (s - l)k. Then G containsk independent cyclesC 1,C 2,...,C k such thats ≤l(C i ) ≤q for 1 ≤i ≤r arnds ≤l(C i ) ≤q + 1 fork -r <i ≤k, where l(Ci) denotes the length ofC i . 相似文献
89.
90.
In this research, a simple, sensitive chemiluminescence (CL) method for the determination of humic acid (HA) in water samples was first developed based on the redox reaction between humic acid and cerium(IV) in the acidic condition. Different with the former redox CL reaction which occurred in alkaline solution, no enhancers were needed and neither precipitation nor a second contamination would occur in the present CL system. Comparing with other spectrometric methods, we find that the proposed analysis system had better applicability and accuracy. Under the optimal experiment conditions, the CL peak height was linear with the concentration of HA in the range of 0.03 to 10.0 microg mL(-1). The detection limit is 0.01 microg mL(-1) (S/N = 3), and the relative standard deviation was 2.3% for 0.5 microg mL(-1) HA solution with eleven repeated measurements. The present CL method was successfully applied to the determination of HA in tap water, spring water and river water samples with good recovery from 90.0 to 110.0%. A possible CL mechanism was proposed based on the results of UV and fluorescence spectrometry and the CL spectrum of HA. It was speculated that the semi-quinone radicals in the excited state were the emitters. 相似文献