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   19795篇
  免费   549篇
  国内免费   18篇
电工技术   259篇
综合类   9篇
化学工业   3681篇
金属工艺   294篇
机械仪表   329篇
建筑科学   1152篇
矿业工程   111篇
能源动力   520篇
轻工业   1470篇
水利工程   162篇
石油天然气   194篇
武器工业   1篇
无线电   1258篇
一般工业技术   3075篇
冶金工业   5114篇
原子能技术   176篇
自动化技术   2557篇
  2022年   126篇
  2021年   225篇
  2020年   182篇
  2019年   230篇
  2018年   279篇
  2017年   268篇
  2016年   330篇
  2015年   246篇
  2014年   403篇
  2013年   1137篇
  2012年   690篇
  2011年   906篇
  2010年   708篇
  2009年   706篇
  2008年   895篇
  2007年   908篇
  2006年   725篇
  2005年   744篇
  2004年   585篇
  2003年   604篇
  2002年   535篇
  2001年   357篇
  2000年   321篇
  1999年   359篇
  1998年   591篇
  1997年   447篇
  1996年   388篇
  1995年   401篇
  1994年   332篇
  1993年   368篇
  1992年   296篇
  1991年   184篇
  1990年   257篇
  1989年   311篇
  1988年   223篇
  1987年   245篇
  1986年   240篇
  1985年   298篇
  1984年   279篇
  1983年   245篇
  1982年   234篇
  1981年   235篇
  1980年   186篇
  1979年   202篇
  1978年   184篇
  1977年   201篇
  1976年   206篇
  1975年   192篇
  1974年   177篇
  1973年   143篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
991.
This study compared 38 distressed and 35 nondistressed families on 2 interaction processes: the continuance of tensions involving the same family members and the spillover of tensions from one family subsystem to another. One parent reported perceptions of family tensions and satisfaction ratings each day for 2 wks. Sequential analyses revealed that distressed, compared with nondistressed, families experienced (1) greater continuance of tensions, particularly tensions that occurred the following day during the same time period, and (2) more spillover, particularly between marital and child-related tensions. Correlations with daily satisfaction ratings indicated that marital dissatisfaction in distressed families is highly related to the occurrence of marital tensions. These data support the importance of examining daily events and multiple family subsystems in order to understand family distress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
992.
993.
994.
995.
Fc gamma RIIa is widely expressed on hematopoietic cells. There are two known allelic polymorphic forms of Fc gamma RIIa, Fc gamma RIIa-R131 and Fc gamma RIIa-H131, which differ in the amino acid at position 131 in the second lg-like domain. In contrast to Fc gamma RIIa-R131, Fc gamma RIIa-H131 binds hlgG2 but not mIgG1, and this differential binding has clinical implications for host defense, autoimmune disease, immunohematologic disease, and response to therapeutic monoclonal antibodies. We identified a novel Fc gamma RIIA genotype in a healthy individual homozygous for Fc gamma RIIA R/R131 in whom a C to A substitution at codon 127 changes glutamine (Q) to lysine (K) in one of the two Fc gamma RIIA genes. This individual's homozygosity for Fc gamma RIIA-R/R131 leads to the prediction that the receptors on her cells would not bind hIgG2. Monocyte and neutrophil phagocytosis of hIgG2-opsonized erythrocytes was significantly higher (P < .05) for cells from this K/Q127, R/R131 individual than for Q/Q127, R/R131 donors. Platelet aggregation stimulated by an mIgG1 anti-CD9 antibody in this individual was significantly different (P < .05) from Q/Q127, H/R131 and Q/Q127, H/H131 donors and similar to Q/Q127, R/R131. Our data show that the K127/R131 receptors have a unique phenotype, binding both hIgG2 and mIgG1. Further functionally significant mutations in human Fc gamma receptors and possible novel mechanisms for inherited differences in disease susceptibility should be sought with unbiased screening methods.  相似文献   
996.
Erb's type limb-girdle muscular dystrophy (LGMD) was identified and clinically studied in detail in a small community living in the Reunion Island (RI). It was linked to chromosome 15q and related to mutations in the muscle specific calpain 3 gene. A series of cases were afterwards clinically and genetically identified in the French metropolitan community. The phenotype was identical to the RI type in the great majority of cases, although clinical differences were noticed in a few cases. Six different mutations were identified in the RI families, whereas a series of 39 mutations were detected in the French metropolitan families, all different from those present in the RI patients. Phenotype-genotype correlations were attempted in both communities.  相似文献   
997.
Experiment 1 established conditioned place preference (CPP) control procedures for young precocial domestic fowl (test day age?=?13–25 days). Chicks displayed a preference (greater choice time) for white stimulus cards on first exposure to white versus red cards and equivalent preference for these stimulus cards after 6 exposures. Chicks in Experiment 2 displayed a cocaine CPP at each dose (0.5, 1.0, and 2.0 mg/kg intraperitoneally) after 6 cocaine-red card and 6 saline-white card pairings. This CPP decreased and was no longer significant over 2 additional nonreinforced test days. Experiment 3 results replicated the cocaine CPP (2.0 mg/kg) and demonstrated that the CPP did not develop when cocaine was administered several hours after card exposure. To our knowledge, these results are the first to demonstrate drug CPP in a nonmammalian model and support the notion that drug reinforcement processes are highly conserved. This precocial avian model may prove a useful addition to existing altricial models for the study of determinants of human drug use and abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
998.
Estevez, L., Kehtarnavaz, N., and Wendt, R. III, Interactive Selective and Adaptive Clustering for Detection of Microcalcifications in Mammograms,Digital Signal Processing6(1996), 224–232.This paper presents a clustering algorithm, called interactive selective and adaptive clustering (Isaac), to assist radiologists in looking for small clusters of microcalcifications in mammograms. Isaac is developed to identify suspicious microcalcification regions which are missed by other classification techniques due to false positive samples in the feature space. It comprises two parts: (i) selective clustering and (ii) interactive adaptation. The first part reduces the number of false positives by identifying the microcalcification subspace or domains in the feature space. The second part allows the radiologist to improve results by interactively identifying additional false positive or true negative samples. Clinical evaluations of mammograms indicate the potential of using this algorithm as an effective tool to bring microcalcification areas to the attention of the radiologist during a routine reading session of mammograms.  相似文献   
999.
Blends of medium-volatile or high-volatile coals have been carbonized in a 7 kg oven with low-volatile coals (6–16% VM, dmmf). A comparison is made of the strength and structural properties of these cokes with those of the cokes made under corresponding conditions from the medium or high-volatile coals alone. With increasing levels of addition of the low-volatile coals the tensile strength of the blend cokes generally attains a maximum and then decreases. These strength changes are related to changes in porosity, pore-wall thickness and pore dimensions. Coals which display some degree of plasticity and which are weakly caking improve coke quality by altering the pore-structure due to the combined effects of decreasing the pore diameter and slightly increasing the wall thickness. Those additives which are non-caking act primarily as wall thickeners.  相似文献   
1000.
The effects of an electrical field (12 KV/cm) and elevated temperature (300°C) on the ignition potential of transformer fluids, which are candidate replacements for polychlorinated biphenyls (PCBs), have been studied. The combined results indicate that the chemical composition of the fluids were alerted, often in such a manner as to increase the ease of ignition. Exploratory Fire Research Center for Fire Research national Bureau of Standards  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