全文获取类型
收费全文 | 57342篇 |
免费 | 5860篇 |
国内免费 | 9022篇 |
专业分类
化学 | 17786篇 |
晶体学 | 733篇 |
力学 | 1646篇 |
综合类 | 876篇 |
数学 | 3497篇 |
物理学 | 9936篇 |
综合类 | 37750篇 |
出版年
2024年 | 146篇 |
2023年 | 458篇 |
2022年 | 1238篇 |
2021年 | 1304篇 |
2020年 | 1347篇 |
2019年 | 1265篇 |
2018年 | 1174篇 |
2017年 | 1485篇 |
2016年 | 1489篇 |
2015年 | 2498篇 |
2014年 | 3114篇 |
2013年 | 3751篇 |
2012年 | 4069篇 |
2011年 | 4467篇 |
2010年 | 4253篇 |
2009年 | 4574篇 |
2008年 | 5091篇 |
2007年 | 4824篇 |
2006年 | 4524篇 |
2005年 | 4054篇 |
2004年 | 3098篇 |
2003年 | 2121篇 |
2002年 | 2415篇 |
2001年 | 2298篇 |
2000年 | 2126篇 |
1999年 | 1213篇 |
1998年 | 529篇 |
1997年 | 437篇 |
1996年 | 350篇 |
1995年 | 325篇 |
1994年 | 300篇 |
1993年 | 274篇 |
1992年 | 275篇 |
1991年 | 203篇 |
1990年 | 175篇 |
1989年 | 171篇 |
1988年 | 164篇 |
1987年 | 133篇 |
1986年 | 90篇 |
1985年 | 57篇 |
1984年 | 72篇 |
1983年 | 66篇 |
1982年 | 42篇 |
1981年 | 39篇 |
1980年 | 49篇 |
1979年 | 22篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1959年 | 7篇 |
1936年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Purple Soil distributes extensively and mainly in China. Because of abundant easily weatherable parent rocks/materials and unstable soil structure, and also influenced by parent materials, usage systems, and slope gradients, erosion and sediment production of purple soils are very severe with main fashions of water erosion and gravitational erosion. Basing on observed data in small watersheds, rainfall erosivity,vegetation coverage, previous soil water content, flow and relating factors such as climate, topograph of small watershed,land usage, and soil kinds are all the influence factors of erosion and erodibility of purple soil as well as sediment production and transport in small watershed of purple hilly areas.The effective technological countermeasures of ecosystem restoration, agricultural tillage for water conservation and erosion prevention, agriculture project, and soil changing for fertility and anti-erosion were provided. 相似文献
32.
In this paper, we discuss the local and global existence ofweak solutions for some hyperbolicparabolic systems modellingchemotaxis. 相似文献
33.
34.
根据塑料挤出的特点,在编程实现对型材截面轮廓凸凹性自动判断的基础上,采用射线法与比例间隔法相结合的方法,确定流道入口圆周上型值点的位置.以三次多项式作为流道模腔型曲线的数学模型,依据流线型要求给出的初始、边界条件,得出型曲线的数学方程.构建了挤出模流道的三维参数化曲面模型.有限元分析结果显示,该方法创建的流线型流道模型,其流动稳定性和平顺性都优于直线型流道. 相似文献
35.
36.
分析了影响分光光度分析的因素,从而选择适宜的测量条件及最佳显色反应条件,以提高仪器的灵敏度. 相似文献
37.
We report viscometric data collected in a Couette rheometry on dilute, single‐solvent polystyrene (PS)/dioctyl phthalate (DOP) solutions over a variety of polymer molecular weights (5.5 × 105 ≤ Mw ≤ 3.0 × 106 Da) and system temperatures (288 K ≤ T ≤ 318 K). In view of the essential viscometric features, the current data may be classified into three categories: The first concerns all the investigated solutions at low shear rates, where the solution properties are found to agree excellently with the Zimm model predictions. The second includes all sample solutions, except for high‐molecular‐weight PS samples (Mw ≥ 2.0 × 106 Da), where excellent time–temperature superposition is observed for the steady‐state polymer viscosity at constant polymer molecular weights. No similar superposition applies at a constant temperature but varied polymer molecular weights, however. The third appears to be characteristic of dilute high‐molecular‐weight polymer solutions, for which the effects of temperature on the viscosity curve are further complicated at high shear rates. The implications concerning the relative importance of hydrodynamic interactions, segmental interactions, and chain extensibility with increasing polymer molecular weight, system temperature, and shear rate are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 787–794, 2006 相似文献
38.
Based on the Dyson-Schwinger equations of QCD in the "rainbow" approximation, the fully dressed quarkpropagator Sf(p) is investigated, and then an algebraic parametrization form of the propagator is obtained as a solutionof the equations. The dressed quark amplitudes Af and Bf built up the fully dressed quark propagator and the dynamicalrunning masses Mf defined by Af and Bf for light quarks u, d and s are calculated, respectively. Using the predictedrunning masses Mf, quark condensates <0|q(0)q(0)|0> = -(0.255 GeV)a for u, d quarks, and <0|s s|0> = 0.8<0|q(0)q(0)]0)for s quark, and experimental pion decay constant fπ = 0.093 GeV, the masses of Goldstone bosons K, π, and η are alsoevaluated. The numerical results show that the masses of quarks are dependent on their momentum p2. The fully dressedquark amplitudes Af and Bf have correct behaviors which can be used for many purposes in our future researches onnonperturbative QCD. 相似文献
39.
通过电位-时间曲线的特征,研究了化学镀镍反应初期不同基体材料的催化特征.在同质基体上可以瞬间诱发化学镀反应,而在异质基体上的诱导期因镀液组成不同而发生变化.在异质基体材料中,Pt无催化活性,Pd的诱发时间最长. 相似文献
40.
刘华 《广西民族大学学报》2005,(3)
通过对瑞典导演伯格曼的电影《假面》所进行的电影美学方面的文本分析,探讨存在于人类的言语与沉默之间的哲学与美学关系,并进而探讨电影作为一种语言的形式的本体论意义。 相似文献