全文获取类型
收费全文 | 2787篇 |
免费 | 41篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 278篇 |
金属工艺 | 13篇 |
机械仪表 | 22篇 |
建筑科学 | 46篇 |
矿业工程 | 4篇 |
能源动力 | 18篇 |
轻工业 | 83篇 |
水利工程 | 2篇 |
石油天然气 | 4篇 |
无线电 | 73篇 |
一般工业技术 | 132篇 |
冶金工业 | 1995篇 |
原子能技术 | 4篇 |
自动化技术 | 145篇 |
出版年
2023年 | 7篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 21篇 |
2017年 | 26篇 |
2016年 | 26篇 |
2015年 | 18篇 |
2014年 | 31篇 |
2013年 | 59篇 |
2012年 | 42篇 |
2011年 | 40篇 |
2010年 | 28篇 |
2009年 | 42篇 |
2008年 | 39篇 |
2007年 | 39篇 |
2006年 | 50篇 |
2005年 | 37篇 |
2004年 | 29篇 |
2003年 | 21篇 |
2002年 | 22篇 |
2001年 | 11篇 |
2000年 | 21篇 |
1999年 | 59篇 |
1998年 | 539篇 |
1997年 | 313篇 |
1996年 | 221篇 |
1995年 | 111篇 |
1994年 | 123篇 |
1993年 | 135篇 |
1992年 | 30篇 |
1991年 | 40篇 |
1990年 | 43篇 |
1989年 | 53篇 |
1988年 | 54篇 |
1987年 | 49篇 |
1986年 | 34篇 |
1985年 | 42篇 |
1984年 | 18篇 |
1983年 | 23篇 |
1982年 | 19篇 |
1981年 | 21篇 |
1980年 | 28篇 |
1979年 | 8篇 |
1977年 | 61篇 |
1976年 | 118篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 13篇 |
1972年 | 7篇 |
排序方式: 共有2829条查询结果,搜索用时 0 毫秒
121.
Intrauterine fetal demise is a source of anxiety to both patient and physician. Heretofore, the standard treatment was either careful observation until the patient went into labor or attempt at induction of labor with oxytocin. Unfortunately, oxytocin stimulation has not proven to be uniformly successful for this problem. Prostaglandin E2 suppositories have been shown to be effective in inducing uterine evacuation after intrauterine fetal demise. In the opinion of the authors, this approach will in the future replace the sometimes dangerous and emotionally laden convention of watchful delayed therapy. 相似文献
122.
If a spinal root of a baboon or rhesus monkey is trapped in an initially loose-fitting silicone rubber channel containing two or more platinum electrodes, electrical pulses sent through these electrodes can stimulate nerve fibres close to the cathode and block the resulting impulses close to the anode. We show (1) how anodal break excitation and excitation of fibres outside the silicone rubber channel can be avoided; (2) that an implant 26 months old behaves like a recent one; (3) that in a root containing somatic motor fibres and parasympathetic fibres, all somatic motor fibres can be blocked and most or all parasympathetic fibres excited but not blocked; (4) that provided that the electrodes pass no net direct current, prolonged stimulation with block can be harmless; (5) how block can be achieved in one direction only along a root; (6) that a peripheral nerve can be blocked by the same techniques. 相似文献
123.
124.
The reduction of the metal ion content of river and well water by chemical treatment with Na2FeO4 has been studied.Pb(II), Cu(II), Zn(II) Fe(III), Hg(II), Cd(II) and Cr(III) are reduced to low levels by the addition of Na2FeO4 and its subsequent decomposition to a Fe(OH)3 gel. The odors (presumably due to sulfur compounds) are completely removed, the bacterial action greatly reduced and the sedimentation rate significantly increased by this reagent. 相似文献
125.
Timofeyev MA Wiegand C Kent Burnison B Shatilina ZM Pflugmacher S Steinberg CE 《The Science of the total environment》2004,319(1-3):115-121
Natural organic matter (NOM) isolated from the eutrophic Sanctuary Pond (Point Pelee National Park, Canada) has an adverse impact on amphipod species (Gammarus tigrinus and Chaetogammarus ischnus from Lake Müggelsee, Germany, and Eulimnogammarus cyaneus, from Lake Baikal, Russia). Increases in amphipod mortality, changes in peroxidase activity and increases of heat shock protein (hsp70) expression were observed upon exposure to NOM. The highest resistance to the adverse impact of NOM was observed with the endemic Baikalian amphipod E. cyaneus. However, the mechanisms behind this finding remains obscure. If differences in the sensitivity of the hsp70 antibody may be excluded, different modes of action may be postulated: because the adverse impact of NOM may be caused by reactive oxygen species (ROS) and the NOM itself, the observed differences may be due to the action of ROS alone (with E. cyaneus) and a combination of both adverse modes of action (European species). 相似文献
126.
A simple method for the analysis of polyacrylamide diffusive gradients in thin film (DGT) gels by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), employing a novel use of (115)In internal standardization, has been developed. This method allows the determination of Co, Ni, Cu, Zn, Cd, and Pb concentrations (at the DGT filter face) or fluxes in sediments at a spatial resolution of 100 microm. Single-layered gels, using an optimized laser defocus of 4000 microm at 400 mJ power, showed high precision (generally approximately 10%) and a linear response during solution deployment. Of the elements Sc, In, Ba, La, Ce, and Tb, Ba most closely tracked variations in laser energy and showed the highest analytical precision but could not be used as an internal standard due to its elevated presence in natural sediments. Therefore, internal standardization, necessary to normalize data collected on different days, was carried out using (115)In contained within a second layer of backing gel and dried along with the analyte layer as a dual-gel disk. This multilayered gel standard required a laser defocus setting of 1000 microm and a laser power of approximately 800 mJ. Analytical precision for a 64-spot ablation grid at 100-microm spacing was approximately 10%. Verification of this method was carried out on DGT sediment probes deployed in Priest Pot (English Lake District). Results obtained by conventional slicing techniques and aqueous elution agreed with laser ablation results when the different sampling areas were considered. The elution results varied by a factor of <2, whereas the laser ablation technique showed a variability of approximately 4, indicating localized elevated concentrations of Co. This higher resolution LA-ICPMS method could ultimately lead to an improved understanding of the geochemical processes responsible for metal uptake and release in sediments. 相似文献
127.
In this article, an unreserved restoration solution for fast failure restoration in intelligent photonic networks is proposed. The unreserved restoration scheme is a real-time restoration technique that allows for utilizing network capacity dynamically and with full flexibility. However, it has the disadvantage of having a long restoration time as real-time redials are required after a failure is detected. The restoration time is crucial because long restoration times can result in data loss that is not expected, especially in high-speed networks. The proposed method targets reducing the aggregated optical cross-connect switching time to minimize real-time failure restoration time. With the proposed solution, in an event of failure, the restoration time can be reduced to times that are similar to those achieved in the reserved schemes. Common unreserved schemes have an inherent need for retries because the first try after failure detection and notification cannot always be guaranteed due to lack of network resource. In this paper, an enhanced implementation for the proposed solution is designed and described, which allows the features of the proposed solution to be fully realized and overcomes the inherent drawback of redundant OXC switching events for retries in common unreserved schemes. Through simulation experiments, it is shown that under a given network condition, the real-time path setup time for failure restoration required in the proposed solution can be improved by 68% compared with the common unreserved schemes. 相似文献
128.
129.
Reviews the book, Home and Hospital Psychiatric Treatment by Fred R. Fenton, Lise Tessier, E. L. Struening, Frank A. Smith and Constance Benoit (1982). From 1972 to 1976, Fenton and his associates were involved in a study at the Montreal General Hospital's Department of Psychiatry that sought to compare a home-based psychiatric treatment program with a more traditional inpatient service. Their monograph presents the rationale for the study, describes the methodology employed, presents their findings and conclusions and discusses issues related to home-based treatment programs and their evaluation. From a methodological point of view, the study is not without its flaws. It does however represent an example of good research in a difficult (real world) setting. The study is well documented and findings are presented in a logical and comprehensible fashion. Its length and detail make it suitable for use as a case study in a class dealing with methodology or evaluation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
130.