全文获取类型
收费全文 | 5922篇 |
免费 | 60篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 29篇 |
综合类 | 9篇 |
化学工业 | 239篇 |
金属工艺 | 37篇 |
机械仪表 | 54篇 |
建筑科学 | 63篇 |
矿业工程 | 12篇 |
能源动力 | 62篇 |
轻工业 | 149篇 |
水利工程 | 30篇 |
石油天然气 | 6篇 |
武器工业 | 1篇 |
无线电 | 267篇 |
一般工业技术 | 296篇 |
冶金工业 | 4509篇 |
原子能技术 | 18篇 |
自动化技术 | 206篇 |
出版年
2021年 | 10篇 |
2020年 | 15篇 |
2019年 | 18篇 |
2018年 | 30篇 |
2017年 | 23篇 |
2016年 | 32篇 |
2015年 | 19篇 |
2014年 | 31篇 |
2013年 | 83篇 |
2012年 | 64篇 |
2011年 | 77篇 |
2010年 | 51篇 |
2009年 | 73篇 |
2008年 | 72篇 |
2007年 | 115篇 |
2006年 | 56篇 |
2005年 | 68篇 |
2004年 | 57篇 |
2003年 | 34篇 |
2002年 | 53篇 |
2001年 | 53篇 |
2000年 | 31篇 |
1999年 | 186篇 |
1998年 | 1435篇 |
1997年 | 788篇 |
1996年 | 539篇 |
1995年 | 302篇 |
1994年 | 261篇 |
1993年 | 301篇 |
1992年 | 48篇 |
1991年 | 69篇 |
1990年 | 68篇 |
1989年 | 79篇 |
1988年 | 70篇 |
1987年 | 42篇 |
1986年 | 49篇 |
1985年 | 57篇 |
1984年 | 17篇 |
1983年 | 26篇 |
1982年 | 43篇 |
1981年 | 34篇 |
1980年 | 46篇 |
1979年 | 23篇 |
1978年 | 27篇 |
1977年 | 90篇 |
1976年 | 179篇 |
1975年 | 14篇 |
1974年 | 19篇 |
1973年 | 14篇 |
1972年 | 14篇 |
排序方式: 共有5987条查询结果,搜索用时 343 毫秒
191.
192.
Collins LW 《Computers in healthcare》1991,12(5):39-40
Executives in healthcare have traditionally had a difficult time communicating with their information managers, believing that they themselves must be technically oriented to understand their own IS system. The author argues that it is the chief information officers who must deepen their knowledge of the industry they have decided to pursue. This in turn will help them become more valuable members of the top executive team as it formulates strategic plans. 相似文献
193.
Along 25 km of the Lake Ontario shoreline near Toronto, Ontario, small coastal embayments (0.4–32 ha) have been constructed or modified by lake-infilling to restore warmwater fish habitat. The variation in thermal habitat quality for warmwater fishes among these embayments is very high; temperatures range from those found within a small pond to those of much cooler Lake Ontario. Since meteorological conditions and surface heat fluxes are almost identical, the temperature variation among embayments must be caused by differences in bathymetry or exchange with Lake Ontario. However, a previous study on these embayments found paradoxically that temperatures were not strongly associated with channel size or embayment bathymetry. This paper resolves the paradox by showing that flushing times for almost all of the constructed embayments were less than 1 day, and often less than 12 h. With so little time to warm within the embayments, water temperatures of almost all embayments remained very close to the temperatures of the adjacent lake waters. The coldest embayments connected directly to open Lake Ontario and warmer embayments connected to Lake Ontario through other embayments or protected harbors, where the inflowing water from Lake Ontario had already substantially warmed. To allow embayments along the exposed shoreline of Toronto to reach acceptable temperatures for warmwater fish, we use heat budgets to calculate that average summer flushing times must be increased from their current length of 1.5 to 5.5 h to approximately 30 h. Such changes could be achieved through large reductions in the channel cross section. 相似文献
194.
We introduce new inductive, generative semisupervised mixtures with more finely grained class label generation mechanisms than in previous work. Our models combine advantages of semisupervised mixtures, which achieve label extrapolation over a component, and nearest-neighbor (NN)/nearest-prototype (NP) classification, which achieve accurate classification in the vicinity of labeled samples or prototypes. For our NN-based method, we propose a novel two-stage stochastic data generation, with all samples first generated using a standard finite mixture and then all class labels generated, conditioned on the samples and their components of origin. This mechanism entails an underlying Markov random field, specific to each mixture component or cluster. We invoke the pseudo-likelihood formulation, which forms the basis for an approximate generalized expectation-maximization model learning algorithm. Our NP-based model overcomes a problem with the NN-based model that manifests at very low labeled fractions. Both models are advantageous when within-component class proportions are not constant over the feature space region "owned by" a component. The practicality of this scenario is borne out by experiments on UC Irvine data sets, which demonstrate significant gains in classification accuracy over previous semisupervised mixtures and also overall gains, over KNN classification. Moreover, for very small labeled fractions, our methods overall outperform supervised linear and nonlinear kernel support vector machines. 相似文献
195.
S.N. YaoAuthor Vitae T. Collins Author VitaeP. Jan?ovi? Author Vitae 《Computers & Electrical Engineering》2012,38(4):811-818
A procedure for designing digital Butterworth filters is proposed. The procedure determines the denominator and the numerator of the filter transfer function based on the positions of the poles in the s-plane and zeros in the z-plane, respectively, and calculates the gain factor using a maximum point normalization method. In contrast to some conventional algorithms, the presented procedure is much simpler by directly obtaining the filter with 3-dB frequencies. This makes the presented algorithm a useful tool for determining the boundaries in electronic or communication systems’ frequency responses. Moreover, the proposed algorithm is compatible with high-order transformations which are the limitations of general pole-zero placement techniques. The proposed method is illustrated by the examples of designing the low-pass, high-pass, band-pass, and band-stop filter. 相似文献
196.
A general solution is given to describe the ac field around surface-breaking cracks for arbitrary values of the ratio of skin depth δ to crack depthd. This solution allows accurate interpretation of crack depth from voltage readings taken by a Crack Microgauge instrument in cases where δ andd are comparable. It is shown to agree with asymptotic formulae obtained for the cases where δ/d is very small and very large. Provided that the probe length Δ is large compared with δ, the calculations show that a very good approximation to the crack depth may be obtained, irrespective of the ratio δ/d, by using the thin-skin asymptotic formula $$d = \frac{1}{2}\Delta (V_2 - V_1 )/V_1 $$ whereV 1 andV 2 are probe voltages registered at positions just off and across the crack, respectively. The problem is solved for a crack of infinite aspect ratio which has no opening, but it can be applied with confidence at the centerline of cracks of fairly large aspect ratio. 相似文献
197.
A randomized controlled trial of home care: clinical outcome for five surgical procedures 总被引:1,自引:0,他引:1
The clinical function of patients receiving home care after five surgical procedures was assessed. Hospital patients who normally would have received minimal nursing care at the end of their hospital stay were randomly assigned to an experimental home-care group or a control group who were discharged from hospital after the normal length of stay. Comprisons of "untoward events" (discomfort, infection, delayed healing, or complications) are reported for the two groups in five surgical categories (varicose vein stripping, herniorrhaphy, cholecystectomy, anal and rectal operations and abdominal hysterectomy) where the home-care program operated efficientyl. No apparent differences in the rates of untoward events were noted between hospital and home-care groups. It is concluded that home care should be considered for reasons other than clinical function, such as socio-economic functioning, the wishes of the patient, or more efficient use of hospital space. 相似文献
198.
Rory A Cooper Michael L Boninger Donald M Spaeth Dan Ding Songfeng Guo Alicia M Koontz Shirley G Fitzgerald Rosemarie Cooper Annmarie Kelleher Diane M Collins 《IEEE transactions on neural systems and rehabilitation engineering》2006,14(4):438-455
With about 2.2 million Americans currently using wheeled mobility devices, wheelchairs are frequently provided to people with impaired mobility to provide accessibility to the community. Individuals with spinal cord injuries, arthritis, balance disorders, and other conditions or diseases are typical users of wheelchairs. However, secondary injuries and wheelchair-related accidents are risks introduced by wheelchairs. Research is underway to advance wheelchair design to prevent or accommodate secondary injuries related to propulsion and transfer biomechanics, while improving safe, functional performance and accessibility to the community. This paper summarizes research and development underway aimed at enhancing safety and optimizing wheelchair design. 相似文献
199.
Muraven Mark; Collins R. Lorraine; Morsheimer Elizabeth T.; Shiffman Saul; Paty Jean A. 《Canadian Metallurgical Quarterly》2005,19(3):253
The authors examined whether the reciprocal relationship between alcohol consumption and distress unfolded over time in 2 samples of social drinkers. Participants monitored their alcohol intake and their cognitive and emotional responses to that drinking on hand-held computers. On mornings after drinking, those who had violated their self-imposed limits the day before reported more guilt, even after controlling for acute negative symptoms of drinking and amount consumed. Reciprocally, guilt led to poorer self-regulation of alcohol intake: Greater distress over alcohol consumption was linked to more intake, intoxication, and more limit violations. Individual differences moderated the relationships among limit violations, distress, and drinking. Consistent with the limit violation effect, violating a limit produced distress over consumption among social drinkers, and they responded to that distress by drinking more. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
200.
钨酸催化氧化环己酮合成己二酸 总被引:3,自引:1,他引:3
以钨酸-有机酸性添加剂为催化体系,在无有机溶剂和相转移剂的情况下,催化30%过氧化氢氧化环己酮合成己二酸。当钨酸∶有机酸性添加剂∶环己酮∶过氧化氢=11∶4∶01∶76(摩尔比,钨酸用量为2.5mmol)时,使用有机酸性添加剂来调节钨酸催化活性,结果表明以钨酸-磺酸水杨酸氧化环己酮效果最优,反应8h时己二酸分离产率达86.8%、纯度为99.9%;以间苯二酚或邻苯二酚为添加剂时,己二酸分离产率分别达到85.9%和84.5%,纯度约为100%;而不使用任何添加剂时,己二酸分离产率只有68.1%、纯度为95.2%。当使用磺酸水杨酸、草酸等为有机酸性添加剂时,随反应时间的延长,己二酸分离产率均升高。当磺酸水杨酸用量为2.5mmol时,己二酸分离产率和纯度均较高。钨酸-磺酸水杨酸和钨酸-草酸催化体系重复使用5次后,己二酸分离产率仍分别可达80.2%和80.9%。 相似文献