全文获取类型
收费全文 | 114443篇 |
免费 | 3689篇 |
国内免费 | 2354篇 |
专业分类
化学 | 49952篇 |
晶体学 | 1194篇 |
力学 | 8075篇 |
综合类 | 97篇 |
数学 | 35139篇 |
物理学 | 26029篇 |
出版年
2023年 | 393篇 |
2022年 | 757篇 |
2021年 | 1063篇 |
2020年 | 1057篇 |
2019年 | 1049篇 |
2018年 | 11122篇 |
2017年 | 10845篇 |
2016年 | 7323篇 |
2015年 | 2084篇 |
2014年 | 1924篇 |
2013年 | 2847篇 |
2012年 | 6729篇 |
2011年 | 13480篇 |
2010年 | 7640篇 |
2009年 | 7878篇 |
2008年 | 9064篇 |
2007年 | 10927篇 |
2006年 | 2464篇 |
2005年 | 3216篇 |
2004年 | 3157篇 |
2003年 | 3364篇 |
2002年 | 2387篇 |
2001年 | 1166篇 |
2000年 | 1053篇 |
1999年 | 780篇 |
1998年 | 640篇 |
1997年 | 559篇 |
1996年 | 659篇 |
1995年 | 462篇 |
1994年 | 415篇 |
1993年 | 400篇 |
1992年 | 310篇 |
1991年 | 290篇 |
1990年 | 243篇 |
1989年 | 218篇 |
1988年 | 164篇 |
1987年 | 159篇 |
1986年 | 141篇 |
1985年 | 154篇 |
1984年 | 114篇 |
1983年 | 95篇 |
1982年 | 118篇 |
1981年 | 113篇 |
1980年 | 87篇 |
1979年 | 93篇 |
1978年 | 81篇 |
1977年 | 52篇 |
1976年 | 57篇 |
1975年 | 54篇 |
1973年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
81.
Claudia-Elisabeth Wulz 《Czechoslovak Journal of Physics》2002,52(3):C155-C170
The principal physics goals of the Compact Muon Solenoid experiment under construction at the Large Hadron Collider at CERN in Geneva are reviewed. Procedures to search for the Standard Model Higgs boson, supersymmetric Higgses and other supersymmetric particles are described. 相似文献
82.
激光诱导荧光探测水体中溶解有机物浓度 总被引:2,自引:2,他引:0
用Nd∶YAG激光器的三倍频355 nm光作为激发光源,根据激光诱导荧光(LIF)方法激发并探测污染水体的荧光光谱.通过对荧光光谱的分析处理研究归一化荧光强度,即450 nm处水中溶解有机物(DOM)峰与405 nm处水的拉曼峰的比值,反演溶解有机物浓度.用商品腐殖酸和去离子水配置成已知浓度的溶液代替标准DOM溶液进行标定,得到回归方程.结果证明,DOM的归一化荧光强度与水体中DOM浓度有较好的线性关系,因此LIF方法是对大面积水域水质进行动态遥测的较理想方法. 相似文献
83.
单甲基原位改性SiO2疏水减反膜的制备与性能研究 总被引:1,自引:0,他引:1
在碱性条件下通过TEOS和MTES的共水解缩聚反应制备了单甲基原位改性的SiO2溶胶,并使用提拉法在K9玻璃基片上镀制了疏水减反膜。通过透射电镜(TEM)考察了镀膜溶胶的微结构,分别使用红外光谱(FTIR)分析了薄膜的组分,用原子力显微镜(AFM)观察了薄膜的表面形貌和起伏状况,用紫外可见光谱(UV-vis)考察了薄膜的减反射性能,用接触角仪测量了薄膜对水的接触角。并使用“R-on-1”的方式测量了薄膜在Nd:YAG激光(1 064 nm,1 ns)作用下的损伤阈值。结果表明,通过共水解缩聚反应可以把甲基引入镀膜溶胶簇团中,改善了溶胶簇团的网络结构,使薄膜得到相当好的疏水性能和更好的抗激光损伤性能,同时薄膜能保持较好的减反射性能。 相似文献
84.
直流稳压电源可以将交流电压变换为直流电压,并使之稳定,在我们现实生活中应用很广泛,在实验中我们利用的电学知识,设计制造了一种直流稳压电源。本文简要介绍了这种直流稳压电源波形演示器的设计目的和电路原理,重点阐述了它的制作流程、滤波和稳压原理以及性能测试输出波形。 相似文献
85.
This paper proposes two constructive heuristics for the well-known single-level uncapacitated dynamic lot-sizing problem. The proposed heuristics, called net least period cost (nLPC) and nLPC(i), are developed by modifying the average period cost concept from Silver and Meal's heuristic, commonly known as least period cost (LPC). An improved tie-breaking stopping rule and a locally optimal decision rule are proposed in the second heuristic to enhance performance. We test the effectiveness of the proposed heuristics by using 20 benchmarking test problems frequently used in the literature. Furthermore, we perform a large-scale simulation study involving three factors, 50 experimental conditions, and 100?000 randomly generated problems to evaluate the proposed heuristics against LPC and six other well-known constructive heuristics in the literature. The simulation results show that both nLPC and nLPC(i) produce average holding and setup costs lower than or equal to those of LPC in every one of the 50 experimental conditions. The proposed heuristics also outperform each of the six other heuristics evaluated in all experimental conditions, without an increase in computational requirements. Lastly, considering that both nLPC and nLPC(i) are fairly simple for practitioners to understand and that lot-sizing heuristics have been commonly used in practice, there should be a very good chance for practical applications of the proposed heuristics. 相似文献
86.
87.
Homo-apioneplanocin A was efficiently synthesized via stereoselective hydroxymethylation, regio- and chemoselective hydroboration, and chemoselective oxidation as key steps from d-ribose. 相似文献
88.
Vinyl and diene derivatives of thiolactomycin have been prepared via Horner-Wadsworth-Emmons olefination from protected 5-formyl-3,5-dimethylthiotetronic acid. Several 4-position protecting groups and a variety of phosphonates were evaluated, with MOM protection and β-ketophosphonates yielding the highest ratio of the desired product to deformylated product. 相似文献
89.
In this paper we suggest a unique model for estimating the operating cost of each of three waste-collection systems. Under the traditional system, which is widely used, waste is typically collected in plastic bags and a three-man crew is needed on each vehicle. The other two systems require a one-man crew for vehicle collecting street containers. The side-loader system with fixed body automatically empties street containers into the vehicle body and empties the load at the disposal site. The side-loader system with demountable body allows the separation of the waste collection phase from transport to the disposal site, since the vehicle body can be demounted. We also present two case studies and show how the estimation of operating costs is a critical issue in decisions regarding the type of system to be used for waste collection. 相似文献
90.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime. 相似文献