全文获取类型
收费全文 | 2634篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 6篇 |
化学工业 | 200篇 |
金属工艺 | 10篇 |
机械仪表 | 16篇 |
建筑科学 | 74篇 |
矿业工程 | 1篇 |
能源动力 | 21篇 |
轻工业 | 86篇 |
水利工程 | 12篇 |
石油天然气 | 6篇 |
无线电 | 160篇 |
一般工业技术 | 122篇 |
冶金工业 | 1808篇 |
原子能技术 | 16篇 |
自动化技术 | 113篇 |
出版年
2021年 | 14篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2014年 | 14篇 |
2013年 | 43篇 |
2012年 | 17篇 |
2011年 | 28篇 |
2010年 | 17篇 |
2009年 | 27篇 |
2008年 | 33篇 |
2007年 | 31篇 |
2006年 | 28篇 |
2005年 | 33篇 |
2004年 | 21篇 |
2003年 | 26篇 |
2002年 | 29篇 |
2001年 | 22篇 |
2000年 | 30篇 |
1999年 | 59篇 |
1998年 | 554篇 |
1997年 | 287篇 |
1996年 | 208篇 |
1995年 | 132篇 |
1994年 | 92篇 |
1993年 | 124篇 |
1992年 | 37篇 |
1991年 | 38篇 |
1990年 | 48篇 |
1989年 | 47篇 |
1988年 | 32篇 |
1987年 | 38篇 |
1986年 | 31篇 |
1985年 | 29篇 |
1984年 | 23篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 38篇 |
1979年 | 19篇 |
1978年 | 20篇 |
1977年 | 48篇 |
1976年 | 134篇 |
1975年 | 15篇 |
1974年 | 10篇 |
1973年 | 14篇 |
1972年 | 7篇 |
1970年 | 8篇 |
1966年 | 6篇 |
排序方式: 共有2651条查询结果,搜索用时 15 毫秒
1.
B. Delworth Gardner 《国际水资源开发杂志》2003,19(1):7-19
For more than half a century, in nearly all western states, the regulatory agencies (the State Engineer or equivalent) used impairment of other water rights as the primary criterion for approving or rejecting change applications to move water to higher-valued uses. In recent years, however, protests to change applications have been brought by 'stakeholders' who do not own water rights, but who argue that they are affected by water transfers. Under the impairment rule, these parties do not have statutory standing to protest successfully. But they have brought legal suits to block transfers, and the courts have considered whether additional criteria involving 'impacts on social welfare' are needed to evaluate transfers. State Supreme Court rulings on such suits in Utah and Nevada are reviewed as prototype cases. The Utah court held that additional 'social welfare' criteria must be utilized by the State Engineer in evaluating change applications, whereas the Nevada court held that such criteria were already incorporated in existing water statutes and administrative practice. The critical question raised in the paper is whether existing state regulatory agencies can effectively implement a real 'social welfare' criterion to evaluate change applications. The conclusion is that they probably cannot, and that if they try, water allocations will be politicized to a much greater extent than they are now, and efficient market transfers will be impeded if not completely prevented. 相似文献
2.
IC Wilson TJ Gardner JM DiNatale AM Gillinov WE Curtis DE Cameron 《Canadian Metallurgical Quarterly》1993,106(5):805-810
Leukocyte depletion improves early postischemic ventricular performance in neonatal models of global myocardial ischemia. However, the rate of leukocyte reaccumulation after cardiopulmonary bypass and its subsequent impact on myocardial function is not known. This laboratory study examined the effect of leukocyte depletion on myocardial performance during the initial 6-hour period after bypass in an in situ, in vivo porcine model of neonatal cardiac surgery. Fifteen 3- to 5-day-old piglets (eight control and seven leukocyte depleted animals) were instrumented by placement of left ventricular short-axis sonomicrometry crystals and an intraventricular micromanometer catheter. Mechanical leukocyte depletion was achieved with Pall RC100 filters (Pall Biomedical, Inc., Fajardo, Puerto Rico) in the cardiopulmonary bypass circuit. Neonatal hearts were subjected to 90 minutes of hypothermic ischemia after a single dose of cold crystalloid cardioplegia. Two control animals died after the operation and were excluded from data analysis. Leukocyte filtration reduced the granulocyte count during initial myocardial reperfusion to 0.8% of control values. However, circulating granulocyte counts increased in leukocyte depleted animals throughout the postoperative period, reaching 68% of control values by 6 hours. Despite this rapid return of circulating granulocytes, animals subjected to leukocyte depletion had significantly better preservation of left ventricular performance (measured by preload recruitable stroke work, p < or = 0.02), left ventricular systolic function (measured by end-systolic pressure-volume relationship, p < or = 0.05), and ventricular compliance (p < or = 0.04) during the experiment. These changes in ventricular function were associated with a significant increase in left ventricular water content (p < or = 0.02) and tissue myeloperoxidase activity (p < or = 0.005) in control animals compared with leukocyte depleted animals. This study demonstrates that leukocyte depletion during initial reperfusion results in sustained improvement in postischemic left ventricular function despite the rapid return of granulocytes to the circulation. 相似文献
3.
OBJECTIVE: The aim of this study was to demonstrate the MR characteristics of non-Hodgkin lymphoma of the skull base to help in the differential diagnosis of this neoplasm from other conditions. MATERIALS AND METHODS: MR of five patients, 7-64 years old, with pathologically proved lymphomas of the skull base were reviewed. Three cases had primary skull base lesions involving the sphenoid bone and the cavernous sinus. One case with a nasal cavity lesion involving the skull base and one with a relapsing skull base lesion of previously treated tonsillar lymphoma were included. RESULTS: The lesions had signal intensities that were similar to that of gray matter of brain on both T1- and T2-weighted imaging. Bilateral cavernous sinuses were involved with encasement of internal carotid arteries in every case. Postcontrast MR showed homogeneous enhancement of the tumor with dural infiltration along the planum sphenoidale, clivus, or tentorium. The clivus was destroyed or replaced by tumors in adult cases but in two children the clivus was preserved with intact sphenooccipital synchondrosis. In one case the tumor extended to the extracranial portion through the jugular foramen. CONCLUSION: The MR findings of a permeative lesion of the skull base, invasion of the cavernous sinus without arterial narrowing, infiltration along the dural surface, and an iso- or hypointensity with brain on T2-weighted imaging should suggest lymphoma. 相似文献
4.
Sun J. Gardner M.K. Liu J.W.S. 《IEEE transactions on pattern analysis and machine intelligence》1997,23(10):603-615
The workload of many real time systems can be characterized as a set of preemptable jobs with linear precedence constraints. Typically their execution times are only known to lie within a range of values. In addition, jobs share resources and access to the resources must be synchronized to ensure the integrity of the system. The paper is concerned with the schedulability of such jobs when scheduled on a priority driven basis. It describes three algorithms for computing upper bounds on the completion times of jobs that have arbitrary release times and priorities. The first two are simple but do not yield sufficiently tight bounds, while the last one yields the tightest bounds but has the greatest complexity 相似文献
5.
6.
We show here that the internucleosomal DNA fragmentation, which is a biochemical hallmark of apoptosis, was induced in a cell density-dependent manner in primary culture of adult rat hepatocytes. This DNA fragmentation could be suppressed by a gene expression inhibitor, indicating the active nature of this process. Moreover, the viability changes in high and low cell density cultures showed a tendency corresponding with the incidence of the DNA fragmentation in them. These results suggest that in hepatocytes there may be a cell density-dependent apoptosis mechanism. In this report, we also show that heparin could suppress this DNA fragmentation with high specificity, and the cell death to some extent. 相似文献
7.
Instrumental techniques are described for displaying (a) the spatial distribution of field emission sites on planar high voltage electrodes and (b) the emission current pattern within an individual site. Typically, emission ‘sites‘ are generally composed of three or more ‘sub-sites’ that become temporally unstable at current > 10?7 A. The electron energy spectra of sub-sites are characteristically single peaked, whose half-widths (FWHM) initially vary linearly with applied field: from changes in spectral area with field, substantially linear sub-site F-N plots have been obtained having β values in the range 300–500. 相似文献
8.
Presents a strategy for analyzing social interactive behaviors occurring simultaneously in parallel streams. The standard strategy for representing such data has been interval coding. Interval coding converts the behavioral stream into a sequence of codes representing the behaviors observed in equal length intervals. This strategy is problematic because statistics calculated from interval coded data depend on the arbitrary choice of interval length. An alternative strategy is to represent the behavioral stream in a continuous-time format, using both the sequence of behaviors and their durations. A continuous-time model for social interactive data was applied to observations of mutual gaze between a husband and wife. The analysis uncovered different distributions of event durations in the two partners: The wife looked primarily at the husband and responded sensitively to his gaze behavior, whereas the husband looked primarily away, unresponsive to the wife. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
9.
10.