首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   346965篇
  免费   3341篇
  国内免费   1351篇
电工技术   6347篇
综合类   599篇
化学工业   49178篇
金属工艺   17285篇
机械仪表   13523篇
建筑科学   7725篇
矿业工程   2232篇
能源动力   7649篇
轻工业   23804篇
水利工程   4018篇
石油天然气   7063篇
武器工业   43篇
无线电   39803篇
一般工业技术   73981篇
冶金工业   56182篇
原子能技术   8428篇
自动化技术   33797篇
  2021年   2247篇
  2019年   2118篇
  2018年   11430篇
  2017年   11983篇
  2016年   8273篇
  2015年   3027篇
  2014年   4498篇
  2013年   12118篇
  2012年   9544篇
  2011年   17481篇
  2010年   15029篇
  2009年   14999篇
  2008年   15185篇
  2007年   17037篇
  2006年   7902篇
  2005年   10589篇
  2004年   9018篇
  2003年   8484篇
  2002年   7321篇
  2001年   6918篇
  2000年   6626篇
  1999年   6792篇
  1998年   16340篇
  1997年   11609篇
  1996年   8950篇
  1995年   6866篇
  1994年   6049篇
  1993年   6081篇
  1992年   4409篇
  1991年   4211篇
  1990年   4079篇
  1989年   4059篇
  1988年   3759篇
  1987年   3389篇
  1986年   3395篇
  1985年   3743篇
  1984年   3462篇
  1983年   3218篇
  1982年   3025篇
  1981年   3041篇
  1980年   3031篇
  1979年   2829篇
  1978年   2869篇
  1977年   3144篇
  1976年   4103篇
  1975年   2416篇
  1974年   2380篇
  1973年   2396篇
  1972年   2018篇
  1971年   1781篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
Absorbable and nonabsorbable buried sutures were studied in primary cleft lip repair. Group 1 (N = 56) consisted of patients repaired with buried nonabsorbable material (monofilament nylon). Group 2 (N = 47) consisted of patients repaired with absorbable materials (polyglyconate, polydioxanone). All patients were monitored for 12 months. There were stitch abscesses in Group 1 (14%). There were no abscesses in Group 2. This difference was significant (p = 0.007). Abscesses were located in the suture line with no identifiable distribution. There was no significant difference in the cosmetic appearance of the scars in Groups 1 and 2. These results support the view that absorbable sutures are preferable to nonabsorbable sutures for primary cleft lip repair.  相似文献   
93.
The transverse resonance approach to guided wave analysis is applied to shear horizontal (SH) wave propagation in periodically layered composites. It is found for SH waves that at high values of the guided wavevector β, the wave energy is trapped in the slower of the two media and propagates accordingly at the slower wavespeed. At low values of β, however, the modes demonstrate a clustering behavior, indicative of the underlying Floquet wave structure. The number of modes in a cluster is observed to correlate with the number of unit cells in the layered plate. New physical insights into the behavior of these systems are obtained by analyzing the partial waves of the guided SH modes in terms of Floquet waves. We show that the fast and slow shear waves in the periodically layered composite play an analogous role to the longitudinal and shear partial waves comprising Lamb waves in a homogeneous plate  相似文献   
94.
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre.  相似文献   
95.
In the present study of gas–liquid contactors, mean residence/contact time was calculated from knowledge of superficial velocity and the gas phase hold-up, for various gas rates and impeller geometry and speeds, and compared with values obtained from RTD measurements. A new correlation, involving Flow Number, Froude Number, system geometry and the physical properties, is proposed. This uses the authors data and those available in literature.  相似文献   
96.
97.
A study of the noise performance of gate overlapped polycrystalline silicon thin-film transistors (TFTs) is presented. Low-frequency noise measurements were carried out on n- and p-type samples fabricated by excimer laser crystallization. It is shown that the carrier number fluctuation model applies not only to n-type but also to p-type devices. The density of oxide traps was extracted from the noise measurements and was of the order of 1018-1019 eV-1 cm-3  相似文献   
98.
Capacity-achieving sequences for the erasure channel   总被引:6,自引:0,他引:6  
This paper starts a systematic study of capacity-achieving (c.a.) sequences of low-density parity-check codes for the erasure channel. We introduce a class A of analytic functions and develop a procedure to obtain degree distributions for the codes. We show various properties of this class which help us to construct new distributions from old ones. We then study certain types of capacity-achieving sequences and introduce new measures for their optimality. For instance, it turns out that the right-regular sequence is c.a. in a much stronger sense than, e.g., the Tornado sequence. This also explains why numerical optimization techniques tend to favor graphs with only one degree of check nodes.  相似文献   
99.
The airborne Millimeter-wave Imaging Radiometer (MIR) measurements conducted over the Midwest region of the continental United States during January/February 1997 and over the Alaska-Arctic region during May 1998 are used to estimate column water vapor W<0.8 g/cm/sup 2/ under a clear sky. On board the same aircraft are two other instruments, the Cloud Lidar System (CLS) and MODerate-resolution Imaging Spectrometer (MODIS) Airborne Simulator (MAS), which provide cloud cover information and independent measurements of W, respectively. The MIR-estimated W values are compared and found to be in very good agreement with those measured by rawinsondes at near concurrence. A close correlation is found between the MIR-estimated W and that estimated from the MAS near-IR reflectance ratios. Water surface emissivities at several MIR frequencies are obtained in the process of the W retrieval from several flights over the Midwest lakes. These estimated emissivities compared favorably with values calculated for a calm water surface, which are based on a di-electric permittivity model and MAS-measured surface temperatures. The results from all comparisons strongly demonstrate the soundness of the technique for estimating W.  相似文献   
100.
OBJECTIVE: To evaluate the relationships between patient and physician pretreatment expectations of pain relief and subsequent pain relief reported by chronic pain patients immediately after treatment. DESIGN: Prospective study of consecutive patients undergoing a procedure in a pain clinic for treatment of chronic pain. Patients rated their current pain level and their expectation of pain relief immediately prior to undergoing a procedure (e.g., intravenous drug infusion, nerve block) for the treatment of chronic pain. Simultaneously and independently, the treating physician completed a similar questionnaire. At completion of the procedure, patients rated their current pain level and degree of pain relief. SETTING: University of Washington Multidisciplinary Pain Center procedure suite. PATIENTS: Forty-six consecutive chronic pain patients. INTERVENTION: Intravenous drug infusions and nerve blocks. OUTCOME MEASURES: Current pain and pain relief ratings. RESULTS: Patients' pain relief expectation ratings were not correlated significantly with their postprocedure pain relief ratings or pre-post procedure changes in pain ratings. However, a statistically significant correlation was found between physician expectations of pain relief and patient pain relief ratings and patient pre-post procedure changes in pain. CONCLUSIONS: The results of this study suggest that physicians are better predictors than are patients of patients responses to these procedures and/or that physicians may somehow subtly communicate their expectations to patients during the procedure, and these expectations then influence patient response. Patient pretreatment expectations may not always play a significant role in nonspecific treatment effects.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号