全文获取类型
收费全文 | 26846篇 |
免费 | 687篇 |
国内免费 | 34篇 |
专业分类
电工技术 | 329篇 |
综合类 | 14篇 |
化学工业 | 5930篇 |
金属工艺 | 517篇 |
机械仪表 | 464篇 |
建筑科学 | 1162篇 |
矿业工程 | 332篇 |
能源动力 | 651篇 |
轻工业 | 1725篇 |
水利工程 | 226篇 |
石油天然气 | 245篇 |
无线电 | 1717篇 |
一般工业技术 | 4102篇 |
冶金工业 | 6175篇 |
原子能技术 | 265篇 |
自动化技术 | 3713篇 |
出版年
2022年 | 247篇 |
2021年 | 413篇 |
2020年 | 267篇 |
2019年 | 346篇 |
2018年 | 422篇 |
2017年 | 369篇 |
2016年 | 485篇 |
2015年 | 392篇 |
2014年 | 614篇 |
2013年 | 1662篇 |
2012年 | 937篇 |
2011年 | 1201篇 |
2010年 | 923篇 |
2009年 | 971篇 |
2008年 | 1150篇 |
2007年 | 1066篇 |
2006年 | 974篇 |
2005年 | 883篇 |
2004年 | 745篇 |
2003年 | 711篇 |
2002年 | 707篇 |
2001年 | 487篇 |
2000年 | 390篇 |
1999年 | 448篇 |
1998年 | 448篇 |
1997年 | 433篇 |
1996年 | 479篇 |
1995年 | 447篇 |
1994年 | 451篇 |
1993年 | 438篇 |
1992年 | 431篇 |
1991年 | 272篇 |
1990年 | 410篇 |
1989年 | 387篇 |
1988年 | 336篇 |
1987年 | 405篇 |
1986年 | 348篇 |
1985年 | 443篇 |
1984年 | 465篇 |
1983年 | 398篇 |
1982年 | 375篇 |
1981年 | 297篇 |
1980年 | 299篇 |
1979年 | 357篇 |
1978年 | 299篇 |
1977年 | 240篇 |
1976年 | 219篇 |
1975年 | 245篇 |
1974年 | 218篇 |
1973年 | 224篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Makris Angela P.; Rush Craig R.; Frederich Robert C.; Taylor Alisia C.; Kelly Thomas H. 《Canadian Metallurgical Quarterly》2007,15(2):123
Modafinil is indicated for the management of excessive daytime sleepiness; however, recent studies have examined a broad range of potential uses. Given that clinical uses of modafinil may be expanding, this study compared modafinil and d-amphetamine effects on subjective and performance measures. Across 11 sessions, 11 healthy adults were tested after oral doses of placebo (5 sessions), modafinil (1.75 mg/kg, 3.50 mg/kg, or 7.00 mg/kg), and d-amphetamine (0.035 mg/kg, 0.070 mg/kg, 0.140 mg/kg) under double-blind, randomized conditions. Assessments of cognitive performance and subjective effects were completed before drug administration, 30 min after drug administration, and at hourly intervals after drug administration for 5 hr. Modafinil increased ratings on the Amphetamine and Morphine Benzedrine Group scales of the Addiction Research Center Inventory (ARCI) and increased ratings on the Vigor and Total Positive scales of the Profile of Mood States. d-Amphetamine increased visual analog ratings of feeling stimulated and liking the drug and increased ratings on the Morphine Benzedrine Group scale of the ARCI. Both medications significantly reduced visual analog scale ratings of feeling sleepy, and modafinil decreased ratings on the ARCI Pentobarbital-Chlorpromazine-Alcohol Group scale. Both medications sustained performance that deteriorated across time on the Sternberg Number Recognition Test. Modafinil also enhanced performance rate on the Digit-Symbol Substitution Task above baseline levels and increased response rate on the Repeated Acquisition of Response Sequences Task. These results suggest that modafinil engenders alerting effects and increases performance in healthy non-sleep-deprived individuals comparable with that of d-amphetamine. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
43.
The exact magnetization pattern of magnetic films close to a spin-reorientation transition is difficult to analyze due to the intrinsically three-dimensional (3d) variation of the orientation of the local magnetization. We present a technique how this can be performed, based on the analysis of high quality 2d polarization maps from a single scanning electron microscope with polarization analysis (SEMPA) measurement with tilted sample. The key tool is the statistical distribution of all occurring polarization doublets, visualized in a 2d histogram plot. From the shape of the distribution the type of transition—canted-phase, or coexisting phases—can be inferred. For the canted-phase state, the canting angle can be accurately determined from geometrical considerations. With help of the histogram the image data can be analyzed and the three components of the magnetization can be calculated for most points of the image. For a Co/Pt multilayer film we found a cone state. The magnetization forms a complex pattern consisting of out-of-plane domains while the in-plane magnetization shows a maze pattern. 相似文献
44.
Robert I. McLachlan Stephen Marsland 《Dynamical Systems: An International Journal》2007,22(3):269-290
The Euler equations associated with diffeomorphism groups have received much recent study because of their links with fluid dynamics, computer vision, and mechanics. In this article, we consider the dynamics of N point particles or “blobs” moving under the action of the Euler equations associated with the group of diffeomorphisms of the plane in a variety of different metrics. This dynamical system is already in widespread use in the field of image registration, where the point particles correspond to image landmarks, but its dynamical behavior has not previously been studied. The 2-body problem is always integrable, and we analyze its phase portrait under different metrics. In particular, we show that 2-body capturing orbits (in which the distances between the particles tend to 0 as t → ∞) can occur when the kernel is sufficiently smooth and the relative initial velocity of the particles is sufficiently large. We compute the dynamics of these “dipoles” with respect to other test particles, and supplement the calculations with simulations for larger N that illustrate the different regimes. 相似文献
45.
46.
Claudia Stewart Nicole Lum Robert Hill Robert Stephens Paul Rudnick Lynn Rassmussen 《Journal of The Association for Laboratory Automation》2003,8(2):64-65
Primer walking of cloned DNA is a standard research tool. It has been used in the past to determine the sequence of individual clones of interest. With the expansion of DNA sequencing capacity the need to be able to walk larger numbers of clones has become necessary. Our laboratory is a mid-sized genomics facility. In conjunction with the Advanced Biomedical Computing Center (ABCC) we have developed methods for automating the primer selection, DNA sequencing, contig assembly and sequence analysis for clones arrayed in microtiter format. This approach has allowed us to walk 475 clones (five microtiter plates) selected from a cDNA library. 相似文献
47.
Defends the practice of modifying reprints of journal articles to amend typographical and other errors that can affect meaning. A standard should be developed for dealing with such errors by hand writing corrections, including a list of errata, or issuing professionally corrected reprints with the notation that corrections have been made. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
48.
Almond preferences were produced by giving rats a mixture of almond and sucrose (Experiments 1-4) or saccharin (Experiment 4). A subsequent extinction procedure consisted of either repeated 2-bottle almond versus water tests (Experiment 1) or repeated exposure to almond alone (Experiments 2-4). The main independent variable was whether access to food following a session was given immediately, 30 min later, or 120 min later. No effect of extinction was found in any experiment. An important finding was that varying the delay until food access had no detectable effect. It was concluded that inadvertent flavor-food associations do not maintain preference for the flavor under extinction conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
49.
The Republicans took control of both houses of Congress in November of 1994 for the 1st time in 42 yrs. Although the magnitude of the Clinton Administration's proposed Health Security Act may well have triggered fears of overcontrol, it is clear that the delivery of psychological care will be changed dramatically by the combined forces of federal and state health reform. R. J. Resnick, President of the American Psychological Association, has appointed the Task Force on Education and Training for Work in Organized Delivery Systems to look at how psychological health care is provided in the new and evolving systems, and to examine how current training programs prepare new psychologists to practice in and around organized health care systems. Dr. Resnick is similarly concerned about standardization of training, training in nontraditional areas of competence, and increased federal recognition and funding of training in psychology. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
50.