全文获取类型
收费全文 | 8632篇 |
免费 | 108篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 139篇 |
综合类 | 4篇 |
化学工业 | 848篇 |
金属工艺 | 109篇 |
机械仪表 | 141篇 |
建筑科学 | 164篇 |
矿业工程 | 32篇 |
能源动力 | 105篇 |
轻工业 | 692篇 |
水利工程 | 42篇 |
石油天然气 | 22篇 |
无线电 | 794篇 |
一般工业技术 | 980篇 |
冶金工业 | 3844篇 |
原子能技术 | 109篇 |
自动化技术 | 716篇 |
出版年
2021年 | 47篇 |
2019年 | 45篇 |
2018年 | 51篇 |
2017年 | 56篇 |
2016年 | 73篇 |
2015年 | 51篇 |
2014年 | 82篇 |
2013年 | 183篇 |
2012年 | 164篇 |
2011年 | 226篇 |
2010年 | 194篇 |
2009年 | 206篇 |
2008年 | 227篇 |
2007年 | 232篇 |
2006年 | 199篇 |
2005年 | 202篇 |
2004年 | 185篇 |
2003年 | 162篇 |
2002年 | 142篇 |
2001年 | 148篇 |
2000年 | 163篇 |
1999年 | 222篇 |
1998年 | 950篇 |
1997年 | 605篇 |
1996年 | 456篇 |
1995年 | 279篇 |
1994年 | 259篇 |
1993年 | 313篇 |
1992年 | 148篇 |
1991年 | 152篇 |
1990年 | 145篇 |
1989年 | 161篇 |
1988年 | 145篇 |
1987年 | 121篇 |
1986年 | 139篇 |
1985年 | 122篇 |
1984年 | 87篇 |
1983年 | 91篇 |
1982年 | 81篇 |
1981年 | 69篇 |
1980年 | 75篇 |
1979年 | 79篇 |
1978年 | 79篇 |
1977年 | 136篇 |
1976年 | 236篇 |
1975年 | 58篇 |
1974年 | 56篇 |
1973年 | 53篇 |
1972年 | 37篇 |
1971年 | 36篇 |
排序方式: 共有8741条查询结果,搜索用时 250 毫秒
121.
The present study is based on the hypothesis that patients with recurrent attacks of aphonia differ from those with non-recurring attacks of aphonia in their anxiety levels, social assertiveness and stress-coping strategies. A comparison was made between 21 women with recurring aphonia and 19 women with non-recurring aphonia with respect to these three factors. Seventeen healthy women served as volunteers. Compared to patients with non-recurring aphonias, patients with recurring aphonias exhibited a significantly higher level of anxiety and significantly more respect for social norms and codes of propriety. Their coping was also characterized by a higher escape tendency. Patients with recurring aphonias also reported a significantly higher number of problems in their private lives within the preceding 5-year period. In therapy patients should be encouraged to reflect upon a possible rigidity toward social norms and better understand fears regarding conflicts in personal relationships. 相似文献
122.
Raybon G. Young M.G. Koren U. Miller B.I. Chien M. Zirngibl M. Dragone C. Froberg N.M. Burrus C.A. 《Electronics letters》1995,31(14):1147-1149
Five wavelength multiplexed pulse streams are generated in an integrated 16×1 laser modulator array by sinusoidally driving five of the potential 16 electroabsorption modulators. At a repetition rate of 2.5 GHz, near transform-limited pulses spaced in wavelength over 7.6 nm are observed. Pseudorandom coding of one channel is achieved by applying an electrical RZ data signal to the modulator 相似文献
123.
124.
KL Miller 《Canadian Metallurgical Quarterly》1994,6(4):785-803
Endocrine disorders in critically ill infants and children can be the manifestation of an existing but previously unrecognized condition, or hormonal derangements precipitated by deleterious effects on endocrine function of a critical illness or its prescribed therapy. To achieve successful resolution of these crises, a general understanding of various endocrine dysfunctions, clinical symptomatology, diagnosis, and medical and nursing management is essential. 相似文献
125.
This paper studies the transient behavior of an adaptive near-far resistant receiver for direct-sequence (DS) code-division multiple-access (CDMA) known as the minimum mean-squared error (MMSE) receiver. This receiver structure is known to be near-far resistant and yet does not require the large amounts of side information that are typically required for other near-far resistant receivers. In fact, this receiver only requires code timing on the one desired signal. The MMSE receiver uses an adaptive filter which is operated in a manner similar to adaptive equalizers. Initially there is a training period where the filter locks onto the signal that is sending a known training sequence. After training, the system can then switch to a decision-directed mode and send actual data. This work examines the length of the training period needed as a function of the number of interfering users and the severity of the near-far problem. A standard least mean-square (LMS) algorithm is used to adapt the filter and so the trade-off between convergence and excess mean-squared error is studied. It is found that in almost all cases a step size near 1.0/(total input power) gives the best speed of convergence with a reasonable excess mean-squared error. Also, it is shown that the MMSE receiver can tolerate a 30-40 dB near-far problem without excessively long convergence time 相似文献
126.
127.
Handling delays in control systems is difficult and is of long-standing interest. It is well known that, given a finite-dimensional linear time-invariant (FDLTI) plant and controller forming a strictly proper stable feedback connection, closed-loop stability will be maintained under a small delay in the feedback loop, although most closed loop systems become unstable for large delays. One previously unsolved fundamental problem in this context is whether, for a given FDLTI plant, an arbitrarily large delay margin can be achieved using LTI control. Here, we adopt a frequency domain approach and demonstrate that, for a strictly proper real rational plant, there is a uniform upper bound on the delay that can be tolerated when using an LTI controller, if and only if the plant has at least one closed right half plane pole not at the origin. We also give several explicit upper bounds on the achievable delay margin, and, in some special cases, demonstrate that these bounds are tight. 相似文献
128.
Powertrain hybridization as well as electrical energy management are imposing new requirements on electrical storage systems in vehicles. This paper characterizes the associated vehicle attributes and, in particular, the various levels of hybrids. New requirements for the electrical storage system are derived, including: shallow-cycle life, high dynamic charge acceptance particularly for regenerative braking and robust service life in sustained partial-state-of-charge usage. Lead/acid, either with liquid or absorptive glass-fibre mat electrolyte, is expected to remain the predominant battery technology for 14 V systems, including micro-hybrids, and with a cost-effective battery monitoring system for demanding applications. Advanced AGM batteries may be considered for mild or even medium hybrids once they have proven robustness under real-world conditions, particularly with respect to cycle life at partial-states-of-charge and dynamic charge acceptance. For the foreseeable future, NiMH and Li-ion are the dominating current and potential battery technologies for higher-functionality HEVs. Li-ion, currently at development and demonstration stages, offers attractive opportunities for improvements in performance and cost. Supercapacitors may be considered for pulse power applications. Aside from cell technologies, attention to the issue of system integration of the battery into the powertrain and vehicle is growing. Opportunities and challenges for potential “battery pack” system suppliers are discussed. 相似文献
129.
Facial muscle activity and self-reports were examined for racial bias in 3 studies. In the first 2 experiments, While participants imagined cooperating with a Black or White partner. Experiment 1 manipulated reward structure in the context of cooperating with a deficient partner. Experiment 2 manipulated partner deficiency and willingness to expend compensatory effort. On both facial EMG and self-report measures, joint rewards produced more negative affect than independent rewards. However, all partners were liked more when they were willing to try to compensate for their deficits. In addition, more liking was reported for Black partners, but EMG activity indicated bias against Blacks. Experiment 3 investigated individual differences in prejudice. Again, a greater preference for Blacks than Whites occurred on self-report measures, but in their facial muscle activity, high-prejudiced participants exhibited bias against Blacks. 相似文献
130.
A common debugging strategy involves reexecuting a program (on a given input) over and over, each time gaining more information about bugs. Such techniques can fail on message-passing parallel programs. Because of nondeterminacy, different runs on the given input may produce different results. This nonrepeatability is a serious debugging problem, since an execution cannot always be reproduced to track down bugs. This paper presents a technique for tracing and replaying message-passing programs. By tracing the order in which messages are delivered, a reexecution can be forced to deliver messages in their original order, reproducing the original execution. To reduce the overhead of such a scheme, we show that the delivery'order of only messages involved inraces need be traced (and not every message). Our technique makes run-time decisions to detect and trace racing messages and is usuallyoptimal in the sense that the minimal number of racing messages is traced. Experiments indicate that only 1% of the messages are often traced, gaining a reduction of two orders of magnitude over traditional techniques that trace every message. These traces allow an execution to be reproduced any number of times for debugging. Our work is novel in that we adaptively decide what to trace, and trace only those messages that introduce nondeterminacy. With our strategy, large reductions in trace size allow long-running programs to be replayed that were previously unmanageable. In addition, the reduced tracing requirements alleviate tracing bottle-necks, allowing executions to be debugged with substantially lower execution time overhead.This work was supported in part by National Science Foundation grants CCR-8815928 and CCR-9100968, Office of Naval Research grant N00014-89-J-1222, and a grant from Sequent Computer Systems, Inc. 相似文献