全文获取类型
收费全文 | 32587篇 |
免费 | 994篇 |
国内免费 | 65篇 |
专业分类
电工技术 | 358篇 |
综合类 | 35篇 |
化学工业 | 6500篇 |
金属工艺 | 852篇 |
机械仪表 | 627篇 |
建筑科学 | 1854篇 |
矿业工程 | 247篇 |
能源动力 | 1012篇 |
轻工业 | 2832篇 |
水利工程 | 327篇 |
石油天然气 | 171篇 |
武器工业 | 2篇 |
无线电 | 2116篇 |
一般工业技术 | 5177篇 |
冶金工业 | 6640篇 |
原子能技术 | 322篇 |
自动化技术 | 4574篇 |
出版年
2021年 | 351篇 |
2020年 | 332篇 |
2019年 | 399篇 |
2018年 | 488篇 |
2017年 | 505篇 |
2016年 | 519篇 |
2015年 | 462篇 |
2014年 | 736篇 |
2013年 | 2161篇 |
2012年 | 1244篇 |
2011年 | 1593篇 |
2010年 | 1173篇 |
2009年 | 1263篇 |
2008年 | 1439篇 |
2007年 | 1470篇 |
2006年 | 1259篇 |
2005年 | 1175篇 |
2004年 | 1055篇 |
2003年 | 1024篇 |
2002年 | 1031篇 |
2001年 | 620篇 |
2000年 | 560篇 |
1999年 | 517篇 |
1998年 | 528篇 |
1997年 | 456篇 |
1996年 | 534篇 |
1995年 | 557篇 |
1994年 | 524篇 |
1993年 | 528篇 |
1992年 | 475篇 |
1991年 | 315篇 |
1990年 | 429篇 |
1989年 | 428篇 |
1988年 | 380篇 |
1987年 | 421篇 |
1986年 | 384篇 |
1985年 | 515篇 |
1984年 | 498篇 |
1983年 | 452篇 |
1982年 | 470篇 |
1981年 | 451篇 |
1980年 | 357篇 |
1979年 | 372篇 |
1978年 | 334篇 |
1977年 | 308篇 |
1976年 | 271篇 |
1975年 | 321篇 |
1974年 | 244篇 |
1973年 | 279篇 |
1972年 | 156篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
81.
82.
Nikolay Kardjilov Ingo Manke Robin Woracek André Hilger John Banhart 《Materials Today》2018,21(6):652-672
Imaging techniques based on neutron beams are rapidly developing and have become versatile non-destructive analyzing tools in many research fields. Due to their intrinsic properties, neutrons differ strongly from electrons, protons or X-rays in terms of their interaction with matter: they penetrate deeply into most common metallic materials while they have a high sensitivity to light elements such as hydrogen, hydrogenous substances, or lithium. This makes neutrons perfectly suited probes for research on materials that are used for energy storage and conversion, e.g., batteries, hydrogen storage, fuel cells, etc. Moreover, their wave properties can be exploited to perform diffraction, phase-contrast and dark-field imaging experiments. Their magnetic moment allows for resolving magnetic properties in bulk samples. This review will focus on recent applications of neutron imaging techniques in both materials research and fundamental science illustrated by examples selected from different areas. 相似文献
83.
84.
Aphids have long been recognized as good phytochemists. They are small sap-feeding plant herbivores with complex life cycles that can involve cyclical parthenogenesis and seasonal host plant alternation, and most are plant specialists. Aphids have distinctive traits for identifying and exploiting their host plants, including the expression of polyphenisms, a form of discrete phenotypic plasticity characteristic of insects, but taken to extreme in aphids. In a relatively small number of species, a social polyphenism occurs, involving sub-adult “soldiers” that are behaviorally or morphologically specialized to defend their nestmates from predators. Soldiers are sterile in many species, constituting a form of eusociality and reproductive division of labor that bears striking resemblances with other social insects. Despite a wealth of knowledge about the chemical ecology of non-social aphids and their phytophagous lifestyles, the molecular and chemoecological mechanisms involved in social polyphenisms in aphids are poorly understood. We provide a brief primer on aspects of aphid life cycles and chemical ecology for the non-specialists, and an overview of the social biology of aphids, with special attention to chemoecological perspectives. We discuss some of our own efforts to characterize how host plant chemistry may shape social traits in aphids. As good phytochemists, social aphids provide a bridge between the study of insect social evolution sociality, and the chemical ecology of plant-insect interactions. Aphids provide many promising opportunities for the study of sociality in insects, and to understand both the convergent and novel traits that characterize complex sociality on plants. 相似文献
85.
Jason M. Lonergan Charmayne Lonergan Joshua Silverstein Pornsinee Cholsaipant John McCloy 《Journal of the American Ceramic Society》2020,103(6):3610-3619
Sulfur trioxide (SO3) additions, up to 3.0 mass%, were systematically investigated for effects on the physical properties of sodium borosilicate glass melted in air, with a sulfur-free composition of 50SiO2–10Al2O3–12B2O3–21Na2O–7CaO (mass%). Solubility measurements, using electron microscopy chemical analysis, determined the maximum loading to be ~1.2 mass% SO3. It was found that measured sulfur (here as sulfate) additions up to 1.18 mass% increased the glass transition temperature by 3%, thermal diffusivity by 11%, heat capacity by 10%, and thermal conductivity by 20%, and decreased the mass density by 1%. Structural analysis, performed with Raman spectroscopy, indicated that the borosilicate network polymerized with sulfur additions up to 3.0 mass%, presumably due to Na2O being required to charge compensate the ionic additions, thus becoming unavailable to form non-bridging oxygen in the silicate network. It is postulated that this increased cross-linking of the borosilicate backbone led to a structure with higher dimensionality and average bond energy. This increased the mean free paths and vibration frequency of the phonons, which resulted in the observed increase in thermal properties. 相似文献
86.
Dr. Pui-Ying Lam Dr. Peter Kutchukian Rajan Anand Dr. Jason Imbriglio Dr. Christine Andrews Hugo Padilla Anita Vohra Sarah Lane Dann L. Parker Jr. Dr. Ivan Cornella Taracido Dr. Douglas G. Johns Dr. Manu Beerens Dr. Calum A. MacRae John P. Caldwell Dr. Steve Sorota Dr. Aarti Asnani Dr. Randall T. Peterson 《Chembiochem : a European journal of chemical biology》2020,21(13):1905-1910
Doxorubicin is a highly effective chemotherapy agent used to treat many common malignancies. However, its use is limited by cardiotoxicity, and cumulative doses exponentially increase the risk of heart failure. To identify novel heart failure treatment targets, a zebrafish model of doxorubicin-induced cardiomyopathy was previously established for small-molecule screening. Using this model, several small molecules that prevent doxorubicin-induced cardiotoxicity both in zebrafish and in mouse models have previously been identified. In this study, exploration of doxorubicin cardiotoxicity is expanded by screening 2271 small molecules from a proprietary, target-annotated tool compound collection. It is found that 120 small molecules can prevent doxorubicin-induced cardiotoxicity, including 7 highly effective compounds. Of these, all seven exhibited inhibitory activity towards cytochrome P450 family 1 (CYP1). These results are consistent with previous findings, in which visnagin, a CYP1 inhibitor, also prevents doxorubicin-induced cardiotoxicity. Importantly, genetic mutation of cyp1a protected zebrafish against doxorubicin-induced cardiotoxicity phenotypes. Together, these results provide strong evidence that CYP1 is an important contributor to doxorubicin-induced cardiotoxicity and highlight the CYP1 pathway as a candidate therapeutic target for clinical cardioprotection. 相似文献
87.
Can Li John P. Eason Markus G. Drouven Ignacio E. Grossmann 《American Institute of Chemical Engineers》2020,66(6):e16933
In this article, we study shale gas pad development under natural gas price uncertainty. We optimize the sequence of operations, gas curtailment, and storage on a single pad to maximize the net present value. The optimization problem is formulated as an mixed-integer linear programming model, which is similar to the one proposed by Ondeck et al. We investigate how natural gas price uncertainty affects the operation strategy in the pad development. Both two-stage and multistage stochastic programming are used as the mathematical framework to hedge against uncertainty. Our case study shows that there is value of using stochastic programming when the price variance is high. However, when the variance of the price is low, solving the stochastic programming problems does not create additional value compared with solving the deterministic problem. 相似文献
88.
Two groups′ research initiated to address two very different questions on problems of basic chemical research led, after much effort on catalyst development and studies of reaction mechanism, to the discovery and development of the coupling of amines with aryl halides in a practical fashion. 相似文献
89.
Journal of Materials Science - The pore fluid within many concretes is highly alkaline and rich in reduced sulfur species, but the influence of such alkaline-sulfide solutions on the surface film... 相似文献
90.