全文获取类型
收费全文 | 22902篇 |
免费 | 794篇 |
国内免费 | 84篇 |
专业分类
电工技术 | 293篇 |
综合类 | 44篇 |
化学工业 | 5148篇 |
金属工艺 | 478篇 |
机械仪表 | 460篇 |
建筑科学 | 1719篇 |
矿业工程 | 160篇 |
能源动力 | 691篇 |
轻工业 | 2137篇 |
水利工程 | 182篇 |
石油天然气 | 56篇 |
武器工业 | 1篇 |
无线电 | 1487篇 |
一般工业技术 | 4177篇 |
冶金工业 | 2772篇 |
原子能技术 | 141篇 |
自动化技术 | 3834篇 |
出版年
2023年 | 152篇 |
2022年 | 308篇 |
2021年 | 535篇 |
2020年 | 312篇 |
2019年 | 327篇 |
2018年 | 493篇 |
2017年 | 426篇 |
2016年 | 531篇 |
2015年 | 479篇 |
2014年 | 690篇 |
2013年 | 1506篇 |
2012年 | 1083篇 |
2011年 | 1519篇 |
2010年 | 1094篇 |
2009年 | 1044篇 |
2008年 | 1269篇 |
2007年 | 1099篇 |
2006年 | 941篇 |
2005年 | 865篇 |
2004年 | 774篇 |
2003年 | 690篇 |
2002年 | 661篇 |
2001年 | 393篇 |
2000年 | 376篇 |
1999年 | 412篇 |
1998年 | 410篇 |
1997年 | 372篇 |
1996年 | 341篇 |
1995年 | 294篇 |
1994年 | 302篇 |
1993年 | 297篇 |
1992年 | 251篇 |
1991年 | 215篇 |
1990年 | 201篇 |
1989年 | 231篇 |
1988年 | 186篇 |
1987年 | 177篇 |
1986年 | 174篇 |
1985年 | 241篇 |
1984年 | 215篇 |
1983年 | 185篇 |
1982年 | 169篇 |
1981年 | 196篇 |
1980年 | 130篇 |
1979年 | 148篇 |
1978年 | 143篇 |
1977年 | 127篇 |
1976年 | 138篇 |
1975年 | 120篇 |
1974年 | 105篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
91.
Norman Fenton Martin Neil William Marsh Peter Hearty Łukasz Radliński Paul Krause 《Empirical Software Engineering》2008,13(5):499-537
Standard practice in building models in software engineering normally involves three steps: collecting domain knowledge (previous
results, expert knowledge); building a skeleton of the model based on step 1 including as yet unknown parameters; estimating
the model parameters using historical data. Our experience shows that it is extremely difficult to obtain reliable data of
the required granularity, or of the required volume with which we could later generalize our conclusions. Therefore, in searching
for a method for building a model we cannot consider methods requiring large volumes of data. This paper discusses an experiment
to develop a causal model (Bayesian net) for predicting the number of residual defects that are likely to be found during
independent testing or operational usage. The approach supports (1) and (2), does not require (3), yet still makes accurate
defect predictions (an R
2 of 0.93 between predicted and actual defects). Since our method does not require detailed domain knowledge it can be applied
very early in the process life cycle. The model incorporates a set of quantitative and qualitative factors describing a project
and its development process, which are inputs to the model. The model variables, as well as the relationships between them,
were identified as part of a major collaborative project. A dataset, elicited from 31 completed software projects in the consumer
electronics industry, was gathered using a questionnaire distributed to managers of recent projects. We used this dataset
to validate the model by analyzing several popular evaluation measures (R
2, measures based on the relative error and Pred). The validation results also confirm the need for using the qualitative factors
in the model. The dataset may be of interest to other researchers evaluating models with similar aims. Based on some typical
scenarios we demonstrate how the model can be used for better decision support in operational environments. We also performed
sensitivity analysis in which we identified the most influential variables on the number of residual defects. This showed
that the project size, scale of distributed communication and the project complexity cause the most of variation in number
of defects in our model. We make both the dataset and causal model available for research use. 相似文献
92.
93.
The thermal stress on building‐integrated photovoltaic modules (BIPV) in Espoo, Finland, was studied with field‐testing of amorphous silicon modules. Based on these results, the thermal stress at two other European locations (Paris and Lisbon) was estimated. The estimation procedure entailed thermal modelling of heat transfer in the façade with meteorological data as input. The results indicate that the thermal stress on BIPV modules in Lisbon is, in this case, approximately 50% higher that in Espoo and between 80 and 200% higher than in Paris, depending on the activation energy of the degradation process. The difference in stress between a BIPV module and a free‐standing module in Espoo was 50–200%. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
94.
Peter Mertens Christian Stary Konrad Walser Thomas Deelmann Franz Lehner Sebastian Günther Christian Scheer 《WIRTSCHAFTSINFORMATIK》2006,48(4):288-295
Ohne Zusammenfassung 相似文献
95.
Legal liabilities pertaining to the identification and selection of domain experts is an issue that could adversely impact expert systems developers. Problems pertaining to flawed knowledge, improperly defined expertise, and behavioural and psychological impediments are just some of the issues. This paper examines the torts of strict products liability and negligence that system developers could incur as a result of expert-related difficulties. Parallels from legal scholars and federal and state court decisions are discussed relevant to expert system projects and developers. The paper concludes with a presentation of steps that systems developers can take to minimize potential legal liability. 相似文献
96.
A test chamber has been developed in order to provide a small and simple emission testing facility capable of testing construction products in a climate where the important climatic parameters such as temperature, ventilation rate and air velocity can be varied independently around typical indoor values. The test chamber CLIMPAQ is made of panes of window glass. Other main surface materials are stainless steel and eloxated aluminium. The chamber has a volume of 50.9 litres and is designed to meet the requirements for quantifying air pollution. In this investigation human subjects acted as air pollution judges, and chemical characterization of the air pollution was carried out. Carpet, linoleum, wall paint and seal- ant were tested simultaneously in the CLIMPAQ and in four other chambers ranging from a full-scale chamber of 28 m3 to a field and laboratory emission cell of 3.5· 10?5m3. Product ranking is the same in all chambers for the sensory measurements. Emission rates based on sensory measurements differ for all products less than 100 % except for tests in a 3-litre chamber where emission rates were higher. Chemical measurements differ up to approximately 10 times for the same product in different chambers. Deviations appear to be the result of different environmental parameters in the various chambers. Low air concentrations or high specific ventilation rates seem to increase emissions, while differences in air velocities and sink properties may also be the cause of differences in emission rates. 相似文献
97.
TK Nordt M Moser B Kohler J Ruef K Peter W Kübler C Bode 《Canadian Metallurgical Quarterly》1998,80(6):881-886
RATIONALE: Reocclusion after thrombolysis diminishes the benefits of early reperfusion after acute myocardial infarction (AMI). No clinical or laboratory variables have been identified as predictors for reocclusion yet. METHODS AND RESULTS: To evaluate hemostatic variables as potential risk determinants platelet aggregation (PA, representing platelet activity), thrombin/antithrombin complexes (TAT, representing thrombin generation), and plasminogen activator inhibitor type 1 (PAI-1, representing endogenous fibrinolysis) were determined in 31 patients with AMI at 0, 1, 2. and 12 h after the start of thrombolysis as well as at hospital discharge. Reocclusion (defined as reinfarction or angiographically confirmed, clinically silent coronary reocclusion) occurred in 5 patients within 5-14 days and in 8 patients within 1 year. TAT plasma concentrations were lower in patients with reocclusion than in those without (9.9+/-5.7 vs. 22.9+/-22.2 ng/ml at 2 h, 6.5+/-3.1 vs. 1 1.2+/-6.4 ng/ml at 12 h, means+/-SD, p <0.05 each). Neither concentration nor activity of PAI-1 in plasma differed between both patient groups. However, both slope and maximum of PA (induced by 2 micromol/l ADP) were augmented in patients with reocclusion (slope: 39.4+/-1.7 vs. 32.5+/-7.4 at 2 h, p <0.001; 42.6+/-2.6 vs. 36.6+/-8.9 at 12 h, p <0.01). Results were independent of the thrombolytic agent used (alteplase or reteplase). A PA slope at 2 h higher than the average slope before thrombolysis (37.2+/-5.7) could be identified as best predictor for early (within 5-14 d, p=0.017, sensitivity 1.00, specificity 0.69) and late reocclusion (within 1 y, p=0.009, 0.88 and 0.74, respectively). CONCLUSIONS: Increased PA following coronary thrombolysis appears to be associated with early and late reocclusion. This marker could be useful in identifying patients who may benefit from more aggressive antiplatelet (such as GP IIb/IIIa receptor antagonists), interventional, or both strategies. 相似文献
98.
99.
Aeromagnetic compensation using neural networks 总被引:1,自引:0,他引:1
Peter M. Williams 《Neural computing & applications》1993,1(3):207-214
Airborne magnetic surveys in geophysical exploration can be subject to interference effects from the aircraft. Principal sources are the permanent magnetism of various parts of the aircraft, induction effects created by the earth's magnetic field and eddy-current fields produced by the aircraft's manoeuvres. Neural networks can model these effects as functions of roll, pitch, heading and their time derivatives, together with vertical acceleration, charging currents to the generator, etc., without assuming an explicit physical model. Separation of interference effects from background regional and diurnal fields can also be achieved in a satisfactory way. 相似文献
100.