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   1667篇
  免费   17篇
电工技术   6篇
化学工业   135篇
金属工艺   4篇
机械仪表   15篇
建筑科学   118篇
矿业工程   2篇
能源动力   8篇
轻工业   47篇
水利工程   4篇
石油天然气   1篇
无线电   34篇
一般工业技术   128篇
冶金工业   1135篇
原子能技术   5篇
自动化技术   42篇
  2022年   5篇
  2021年   6篇
  2020年   4篇
  2019年   5篇
  2018年   8篇
  2017年   7篇
  2016年   7篇
  2015年   11篇
  2014年   4篇
  2013年   34篇
  2012年   20篇
  2011年   22篇
  2010年   13篇
  2009年   13篇
  2008年   18篇
  2007年   16篇
  2006年   21篇
  2005年   14篇
  2004年   12篇
  2003年   14篇
  2002年   12篇
  2001年   15篇
  2000年   17篇
  1999年   41篇
  1998年   335篇
  1997年   193篇
  1996年   129篇
  1995年   74篇
  1994年   83篇
  1993年   70篇
  1992年   27篇
  1991年   26篇
  1990年   23篇
  1989年   31篇
  1988年   26篇
  1987年   33篇
  1986年   28篇
  1985年   25篇
  1984年   8篇
  1983年   11篇
  1982年   10篇
  1981年   12篇
  1980年   19篇
  1977年   35篇
  1976年   87篇
  1971年   3篇
  1967年   3篇
  1926年   3篇
  1920年   3篇
  1919年   3篇
排序方式: 共有1684条查询结果,搜索用时 15 毫秒
1.
2.
3.
The efficacy of an oxidized regenerated cellulose barrier (Interceed) in reducing postoperative adhesion formation and improving reproductive outcome after ovarian surgery was evaluated in a prospective randomized trial. Twenty-nine New Zealand White female rabbits were submitted to a mid-line laparotomy and a standardized surgical incision was made on both ovaries. At random, one ovary was entirely wrapped in a sheet of Interceed, whereas the contralateral ovary was left uncovered. Four weeks following surgery, the rabbits were mated with a male of proven fertility. Two weeks later, a second-look laparotomy was performed by a blinded observer who evaluated the incidence and score of adhesions, the number of corpora lutea in each ovary, the number of embryos in the ipsilateral uterine horn and also calculated the nidation index for each side. Adhesions were observed in 66% of Interceed-covered and in 97% of control ovaries (P < 0.0001). The adhesion score on the Interceed side was significantly lower than on the control side. The nidation index for the Interceed side was significantly higher than for the control side. The authors conclude that, in the rabbit model, Interceed significantly reduces the incidence and score of postoperative ovarian adhesions and significantly improves reproductive outcome.  相似文献   
4.
In this report we reviewed the role of Ultrasonography, Computed Tomography, Magnetic Resonance and 99Tc-Sestamibi Scintigraphy for the detection of abnormal parathyroid glands in patients with biochemical evidence of hyperparathyroidism. We also report our personal experience with CT and RM.  相似文献   
5.
6.
It has previously been shown that the Copenhagen (COP) rat contains several genetic loci that contribute to its mammary tumor-resistant phenotype after 7,12-dimethylbenz(a)anthracene (DMBA) administration. One of these loci, mammary carcinoma susceptibility 1 (Mcs1), is located on the centromeric end of chromosome 2 and appears to act in a semidominant fashion. To confirm the existence and independent action of this locus and also aid in the identification of the physical location of the Mcs1 gene, congenic lines were generated by transferring the Mcs1 COP allele onto a Wistar Furth (WF) genetic background. Male carriers were genotyped using microsatellite markers spanning 20-30 cM of the Mcs1 locus. One of the congenic lines minimally retained the COP allele at D2Mit29 on the centromeric end of chromosome 2 and extended distally to D2Rat201. Heterozygous Mcs1 carrier rats were interbred, and the female offspring were treated with DMBA. The female rats from the Mcs1 congenic line that carried one or two COP alleles of the Mcs1 region had a significantly reduced (65 and 85%, respectively) tumor development (P < 0.001) compared with rats carrying zero COP alleles at this locus. A WF.COP-D2Mit29/D2Rat201 homozygous congenic strain derived at the N10 generation was treated with DMBA, and the COP homozygous rats developed 1.5 +/- 0.3 carcinomas/rat versus 6.3 +/- 0.5 in WF control rats (P < 0.0001). Fine mapping of this congenic interval using several recombinant lines identified three genetic loci within the Mcs1 congenic region that independently supported a tumor resistance phenotype. These genetic loci have been termed Mcs1a, Mcs1b, and Mcs1c. In rats for which each locus was homozygous for the COP allele, tumor development was reduced by approximately 60% compared with littermate controls. The identification of these independent loci within the Mcs1 COP allele provide a model of the genetic complexity of cancer.  相似文献   
7.
The authors report the implementation of deep-submicrometer Si MOSFETs that at room temperature have a unity-current-gain cutoff frequency (fT) of 89 GHz, for a drain-to-source bias of 1.5 V, a gate-to-source bias of 1 V, a gate oxide thickness of 40 Å, and a channel length of 0.15 μm. The fabrication procedure is mostly conventional, except for the e-beam defined gates. The speed performance is achieved through an intrinsic transit time of only 1.8 ps across the active device region  相似文献   
8.
The cardiovascular effects of a partially purified extract of fish oil, enriched in the n-3 series fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were studied in stroke-prone spontaneously hypertensive rats (SHR-SP) fed with high- and low-sodium diets during 5 weeks. Addition of salt to the low-salt control diet at a level commonly found in human food items (6% NaCl of the dry weight of the diet) produced a remarkable rise in blood pressure, an increase in left ventricular weight-to-body weight ratio (LVH-index) and an increase in kidney weight-to-body weight ratio (RH-index). Fish oil (20% of the dry weight of the diet) did not significantly influence the blood pressure or LVH-index or RH-index during the low-salt control diet. However, fish oil completely prevented the remarkable rise in blood pressure and clearly antagonized the rise of both LVH- and RH-indices, induced by the high-salt diet. The fish oil supplementation increased the levels of the polyunsaturated fatty acids of the n-3 series and decreased those of the n-6 series in plasma and kidney, irrespective of the salt content of the diet. Fish oil lowered serum thromboxane B2 concentration by approximately 75%. During the high-salt diet, fish oil markedly decreased water intake and urine volume, and increased urinary sodium concentration by about 60%. Our findings show that, in addition to an antihypertensive effect, fish oil also decreases LVH and RH. These effects appear to be due to an improved ability to excrete sodium and could be explained by the observed changes in the fatty acid composition and metabolism.  相似文献   
9.
Current work on disease states involving the patella has led to increased interest in patellar instability. We reviewed a series of patellar luxations. True trauma-induced luxations are rare. Most cases are recurrent luxations in subjects with a morphological anomaly of the knee extensor system. Because of the growth cartilages, selective therapeutic techniques are needed to stabilize the patella. Recurrent or permanent luxations of the patella result from congenital malformations of the muscles or skeleton. A complete MRI study is highly indicated. The patella can be correctly realigned by surgical release. In cases with femoropatellar dysplasia, which is not specific for children, well conducted rehabilitation therapy often leads to favourable outcome.  相似文献   
10.
The NADPH-dependent metabolism of ifosphamide catalyzed by rat liver microsomes was investigated in order to identify individual P450 enzymes that activate this anti-cancer drug and to ascertain their relationship to the P450 enzymes that activate the isomeric drug cyclophosphamide. Pretreatment of rats with phenobarbital or clofibrate increased by up to 8-fold the activation of both ifosphamide and cyclophosphamide catalyzed by isolated liver microsomes. Studies using P450 form-selective inhibitory antibodies demonstrated that constitutively expressed P450s belonging to subfamily 2C (forms 2C11/2C6) make significant contributions to the activation of both oxazaphosphorines in uninduced male rat liver microsomes, while the phenobarbital-inducible P450 2B1 was shown to be a major catalyst of these activations in phenobarbital-induced microsomes. Pretreatment of rats with dexamethasone increased liver microsomal activation of ifosphamide approximately 6-fold without a corresponding effect on cyclophosphamide activation rates. Ifosphamide activation catalyzed by dexamethasone-induced liver microsomes was minimally inhibited by anti-P450 2B or anti-P450 2C antibodies, but was selectively inhibited by anti-P450 3A antibodies. Selective inhibition of liver microsomal ifosphamide activation was also effected by the macrolide antibiotic triacetyloleandomycin, an inhibitor of several dexamethasone-inducible 3A P450s. These studies establish that a dexamethasone-inducible family 3A P450 can make an important contribution to rat liver microsomal ifosphamide activation, and suggest that dexamethasone pretreatment might provide a useful approach for modulation of ifosphamide metabolism in order to improve its therapeutic efficacy in cancer patients.  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