全文获取类型
收费全文 | 4998篇 |
免费 | 99篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 84篇 |
综合类 | 4篇 |
化学工业 | 612篇 |
金属工艺 | 86篇 |
机械仪表 | 94篇 |
建筑科学 | 67篇 |
矿业工程 | 2篇 |
能源动力 | 204篇 |
轻工业 | 254篇 |
水利工程 | 30篇 |
石油天然气 | 32篇 |
无线电 | 276篇 |
一般工业技术 | 457篇 |
冶金工业 | 2660篇 |
原子能技术 | 15篇 |
自动化技术 | 234篇 |
出版年
2024年 | 5篇 |
2023年 | 35篇 |
2022年 | 55篇 |
2021年 | 116篇 |
2020年 | 78篇 |
2019年 | 76篇 |
2018年 | 113篇 |
2017年 | 88篇 |
2016年 | 99篇 |
2015年 | 69篇 |
2014年 | 90篇 |
2013年 | 250篇 |
2012年 | 174篇 |
2011年 | 164篇 |
2010年 | 118篇 |
2009年 | 108篇 |
2008年 | 96篇 |
2007年 | 79篇 |
2006年 | 77篇 |
2005年 | 54篇 |
2004年 | 51篇 |
2003年 | 62篇 |
2002年 | 45篇 |
2001年 | 45篇 |
2000年 | 48篇 |
1999年 | 106篇 |
1998年 | 876篇 |
1997年 | 452篇 |
1996年 | 325篇 |
1995年 | 197篇 |
1994年 | 140篇 |
1993年 | 203篇 |
1992年 | 37篇 |
1991年 | 39篇 |
1990年 | 42篇 |
1989年 | 32篇 |
1988年 | 53篇 |
1987年 | 50篇 |
1986年 | 37篇 |
1985年 | 37篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 30篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 54篇 |
1976年 | 114篇 |
1975年 | 6篇 |
排序方式: 共有5111条查询结果,搜索用时 15 毫秒
1.
2.
3.
The objective of this study is to determine the economic and operational impact on energy cost of incorporating large photovoltaic (PV) and wind energy conversion systems (WECS) into the electric utility generation mix. In most cases, PV and WECS power outputs are subtracted from the utility load with the expectation that conventional generation would meet the residual load. This approach is valid for small penetration levels and/or for PV and WECS facilities connected near load centers, However, several constraints such as thermal generation characteristics, fuel supply and delivery, spinning reserve requirements, and hydro availability are not adequately represented in this process. To determine the optimal value of large-scale PV and WECS applications, a new methodology that would take into account the aforementioned constraints as well as a more global penetration is developed. Results indicate that while high hydro availability increases PV penetration levels, high ramping rates can also significantly increase penetration levels 相似文献
4.
5.
Various nitroaromatics are successfully reduced to amines with 100% conversion and selectivity in methanol at low temperature (≈5 °C), by using versatile system of 5% Ni–SiO2 catalyst and NaBH4 and in situ generation of Ni boride. The catalytic efficiency of Ni loading (5%, 10% and 15%) with silica or titania as support materials is investigated for reduction of nitrobenzene. The Ni–titania/NaBH4 system recorded lower conversion and selectivity. The IR studies indicate that silica support does not have free –OH group on its surface. Thus the nickel boride is anchored to the silica to facilitate the catalytic process. 相似文献
6.
M. K. Rahman 《Structural and Multidisciplinary Optimization》1994,7(1-2):126-137
A multilevel design scheme for ship's hull girders (longitudinal members between two adjacent transverse frames) is presented in this paper. This design scheme handles, very conveniently, the complexity of using an optimization algorithm for such complex design problems having a large number of design variables, nonlinear constraints dealing with different failure modes and interactions among substructures, and nonlinear design objectives. The conventional multilevel design technique is modified by introducing an approach called constraint coordination to increase the probability of achieving the overall optimum very efficiently.The scheme is demonstrated by application to the structural design of hull girders with simple structural modelling to represent inland waterway ships on which there was a special emphasis in the original research project (Rahman 1991). Three possible panel (consisting of one stiffener and its attached plating) forms; tee stiffened, flat-bar stiffened and corrugated, are optimized to synthesize the hull girder in order to achieve the most efficient structure. The effect of price-structure (labour rate to material price ratio) on the design is also investigated. 相似文献
7.
The feasibility of applying a chemical method based on the formation of 2-alkylcyclobutanone to samples of irradiated soft cheese (Brie and Camembert) was investigated. Significant quantities of 2-dodecylcyclobutanone (DCB) and 2-tetradecylcyclobutanone (TCB) were detected in both types of irradiated cheese and are proposed as qualitative markers. Other members of the cyclobutanone family (decyl- and tetradecenyl-) are also thought to be present but could not be substantiated due to a lack of authentic standards. These compounds were absent from the unirradiated samples. Results also show a significant linear relationship between the irradiation dose (1 to 8 kGy) and the amount of DCB and TCB detected in the cheese. 相似文献
8.
9.
HJ Lee HK Ha MH Kim YK Jeong PN Kim MG Lee JS Kim DJ Suh SG Lee YI Min YH Auh 《Canadian Metallurgical Quarterly》1997,169(2):517-520
OBJECTIVE: The purpose of this study was to evaluate ERCP and CT findings of ectopic drainage of the common bile duct into the duodenal bulb. CONCLUSION: Although rare, the diagnosis of ectopic drainage of the common bile duct into the duodenal bulb is important to prevent inadvertent damage during biliary tract or gastric surgery and to clarify the cause of chronic peptic ulcers. 相似文献
10.
PURPOSE: The purpose of this study was to assess the value of 3-dimensional sonography in the diagnosis of congenital müllerian duct anomalies, which cause infertility, preterm labor, and first trimester abortion. METHODS: A prospective study was undertaken in which 40 patients with histories of repeated spontaneous abortions or infertility were first examined using conventional 2-dimensional sonography or hysterosalpingography. Three-dimensional transvaginal sonography was then performed. RESULTS: Twenty-eight women had müllerian duct abnormalities, and 12 women had normal uterine anatomy. Müllerian duct defects detected in this study were unicornuate uterus (3), bicornuate uterus (3), complete or partial septate uterus (12), arcuate uterus (9), and didelphic uterus (1). The diagnosis of müllerian duct anomalies in these patients was confirmed by laparoscopic and/or hysteroscopic examinations. Three-dimensional sonography demonstrated all congenital uterine abnormalities with a sensitivity and specificity of 100%. Separate uterus and bicornuate uterus could be correctly diagnosed using 3-dimensional sonography in 11 (92%) of 12 cases and 3 (100%) of 3 cases, respectively. These 2 abnormalities were commonly confused with each other using hysterosalpingography and conventional sonography. CONCLUSIONS: Three-dimensional sonography with image reconstruction is less expensive and less invasive than hysterosalpingography for the assessment of uterine anatomy and diagnosis of müllerian duct abnormalities. The ability to visualize both the uterine cavity and the myometrium on a 3-dimensional scan facilitates the diagnosis of uterine anomalies and enables the differentiation of septate from bicornuate uteri for preoperative surgical planning. 相似文献