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   3193篇
  免费   60篇
  国内免费   2篇
电工技术   43篇
综合类   2篇
化学工业   346篇
金属工艺   39篇
机械仪表   49篇
建筑科学   82篇
矿业工程   6篇
能源动力   67篇
轻工业   261篇
水利工程   10篇
石油天然气   23篇
无线电   231篇
一般工业技术   328篇
冶金工业   1573篇
原子能技术   15篇
自动化技术   180篇
  2022年   19篇
  2021年   24篇
  2020年   26篇
  2019年   31篇
  2018年   29篇
  2017年   35篇
  2016年   41篇
  2015年   18篇
  2014年   30篇
  2013年   82篇
  2012年   68篇
  2011年   92篇
  2010年   56篇
  2009年   72篇
  2008年   72篇
  2007年   61篇
  2006年   44篇
  2005年   47篇
  2004年   63篇
  2003年   54篇
  2002年   37篇
  2001年   31篇
  2000年   42篇
  1999年   84篇
  1998年   444篇
  1997年   270篇
  1996年   181篇
  1995年   127篇
  1994年   95篇
  1993年   110篇
  1992年   29篇
  1991年   43篇
  1990年   41篇
  1989年   36篇
  1988年   46篇
  1987年   36篇
  1986年   38篇
  1985年   44篇
  1984年   31篇
  1983年   26篇
  1982年   39篇
  1981年   44篇
  1980年   34篇
  1979年   27篇
  1978年   32篇
  1977年   67篇
  1976年   119篇
  1975年   13篇
  1974年   19篇
  1973年   14篇
排序方式: 共有3255条查询结果,搜索用时 15 毫秒
51.
This study with the rat evaluated the contribution of omega-conotoxin GVIA-(omega-CgTx) and verapamil-sensitive Ca2+ channels in behavioural, antinociceptive and thermoregulatory responses to intracerebroventricular (i.c.v.) injection of [D-Ala2,NMePhe4,Gly-ol5]enkephalin (DAMGO), [D-Pen2,D-Pen5]enkephalin (DPDPE) and dynorphin A-(1-17), which are selective agonists for putative mu, delta and kappa-opioid receptors, respectively. The rats treated with omega-CgTx (8-32 pmol i.c.v.) showed transient, dose-dependent shaking behaviour, hyperalgesia and hypothermia which gradually disappeared within 4 h. The behaviour of the rats was normal by 24 h. Histological examination of brain sections showed morphological alterations of neurons in the hippocampus, medial-basal hypothalamus and pyriform cortex. antinociception, catalepsy and thermoregulatory responses elicited by DAMGO (0.4 and 2.0 nmol) were significantly prolonged and potentiated by verapamil (20 pmol i.c.v. 15 min before) or omega-CgTx (8 pmol 24 h before). Antinociception and hypothermia induced by DPDPE were antagonized by verapamil and omega-CgTx, whereas only omega-CgTx prevented the behavioural arousal observed after DPDPE. Similarly, hypothermia induced by dynorphin A-(1-17) (5.0 nmol) and by the kappa-opioid receptor agonist U50,488H (215 nmol) was antagonized by the two Ca2+ channel blockers but only omega-CgTx prevented the barrel rolling and bizarre postures caused by the opioid peptide.  相似文献   
52.
1. The spontaneously hypertensive rat (SHR) exhibits a lower bodyweight in utero and an exaggerated salt appetite post partum. To determine whether salt appetite is affected by the perinatal environment, we measured the salt appetite of embryo-cross-transferred SHR and Wistar Kyoto (WKY) rats at maturity. 2. One-cell embryos were collected from the oviducts of donor rats and transferred into the oviducts of recipients through the infundibulum. The salt appetite of the resultant female offspring for 0.10 and 0.15 mol/L saline was measured at 20-30 weeks of age. 3. Salt intake of SHR gestated in WKY rats was significantly lower than that of SHR gestated in SHR, while that of WKY rats gestated in SHR was higher than that of WKY rats gestated in WKY rats. 4. Therefore, some maternal factor plays a role in the development of the exaggerated salt appetite of the SHR. This factor is also able to affect the later salt appetite of WKY rat offspring born to SHR surrogates.  相似文献   
53.
Urinary tract abnormalities are fairly common in the perinatal period. Ultrasonography is an effective diagnostic tool for identifying fetal urinary tract anomalies and can be helpful in establishing prognosis and guiding treatment decisions. The sonographer is encouraged to characterize and localize the fetal urinary tract abnormality when identified. In doing so, the correct diagnosis can be selected from the differential possibilities, providing vital clinical information needed to develop a care plan for both the pregnant woman and her fetus.  相似文献   
54.
In a duplicate study during 1987-1991, 478 24-h duplicate samples from 14 homes for elderly people and 10 homes for youth were investigated for their contents of selected harmful substances. The analyses covered 45 active substances of pesticides, 17 PCB-congeners as well as lead, cadmium, and nitrate contents. Pesticides could be detected only in 15% of the investigated samples. The pesticide contents reached max. 8% of the respective FAO/WHO-limits. As the mean intake of the three most important PCB-congeners (sum of the congeners 138, 153, and 180) values of 0.9 and 1.1 micrograms per day and ration or person, respectively, were found. Also in the worst case the daily PCB intake was below the recommended ADI value of the FDA of 1 microgram/kg of body weight. The daily nutritional intake of lead and cadmium via the investigated daily rations reached about 5.6% and 20% of the Provisionally Tolerably Weekly Intake values of the FAO/WHO. The mean nitrate content of the duplicate portions was 101 mg per day and person (median: 79 mg per day and person). Referred to the median value the WHO limit (3.65 mg/kg body weight and day) was exhausted to about 36%.  相似文献   
55.
AIM: The study of quality of life and 24-h monitoring blood pressure data in elderly patients with isolated systolic hypertension (SH) on arifon monotherapy. MATERIALS AND METHODS: 22 patients over 65 (mean age 69.8 +/- 1.3 years) suffering from SH entered the open trial. 24-h monitoring of blood pressure was performed at least 2 weeks after discontinuation of the previous antihypertensive treatment and after 4 weeks of arifon monotherapy (2.5 mg once a day). Quality of life was evaluated according to the standard SIP questionnaire. RESULTS: Arifon 4-week treatment resulted in a significant fall of systolic pressure for 24 hours, day and night (by 16.2, 13.7 and 17.4%, respectively; p < 0.001). Variability of blood pressure did not change much. 24-h index for systolic and diastolic blood pressure increased 2-fold and by 46%, respectively. Moreover, the rate of the systolic pressure growth in the morning hours decreased by 36.7% (p < 0.05). Psychosomatic status by SIP questionnaire changed for the best. CONCLUSION: Arifon is an effective treatment of SH and improves quality of life.  相似文献   
56.
We evaluated the results twenty to twenty-five years after ninety-three consecutive, nonselected Charnley total hip arthroplasties performed with cement by the senior one of us in sixty-nine patients who were less than fifty years old at the time of the procedure. Seventy of the seventy-two hips in the living patients were followed radiographically for at least twenty years. Twenty-seven hips (29 per cent) had a revision or a resection of the prosthesis during the follow-up period. The revision or the resection was performed because of aseptic loosening in twenty-one hips (23 per cent), infection in four (4 per cent), dislocation in one (1 per cent), and fracture of the femur in one. Eighteen acetabular components (19 per cent) and five femoral components (5 per cent) were revised because of aseptic loosening, and an additional fourteen acetabular components (15 per cent) and seven femoral components (8 per cent) demonstrated definite or probable radiographic loosening. The present study demonstrates the long-term durability of total hip arthroplasty performed with cement in an active population of patients. The fixation of the femoral component was found to perform better than that of the acetabular component at twenty to twenty-five years after the procedure.  相似文献   
57.
A DNA fragment containing the recA gene of Gluconobacter oxydans was isolated and further characterized for its nucleotide sequence and ability to functionally complement various recA mutations. When expressed in an Escherichia coli recA host, the G. oxydans recA protein could efficiently function in homologous recombination and DNA damage repair. The recA gene's nucleotide sequence analysis revealed a protein of 344 amino acids with a molecular mass of 38 kDa. We observed an E. coli-like LexA repressor-binding site in the G. oxydans recA gene promoter region, suggesting that a LexA-like mediated response system may exist in G. oxydans. The expression of G. oxydans recA in E. coli RR1, a recA+ strain, surprisingly caused a remarkable reduction of the host wild-type recA gene function, whereas the expression of both Serratia marcescens recA and Pseudomonas aeruginosa recA gene caused only a slight inhibitory effect on function of the host wild-type recA gene product. Compared with the E. coli RecA protein, the identity of the amino acid sequence of G. oxydans RecA protein is much lower than those RecA proteins of both S. marcescens and Pseudomonas aeruginosa. This result suggests that the expression of another wild-type RecA could interfere with host wild-type recA gene's function, and the extent of such an interference is possibly correlated to the identity of the amino acid sequence between the two classes of RecA protein.  相似文献   
58.
59.
Denaturing gradient gel electrophoresis revealed changes in the bacterial species obtained from enrichment cultures with different inoculum dilutions. This inoculum dilution enrichment approach may facilitate the detection and isolation of a greater number of bacterial species than traditional enrichment techniques.  相似文献   
60.
Naturally produced methane shows different delta 13C-values with respect to its origin, e.g., geological or biological. Methane-production of ruminants is considered to be the dominant source from the animal kingdom. Isotopic values of rumen methane--given in literature--range between -80/1000 and -50/1000 and are related to feed composition and also sampling techniques. Keeping cows, camels and sheep under identical feed conditions and sampling rumen gases via implanted fistuale we compared delta PDB 13C-values of methane and CO2 between the species. Referring to mean values obtained from 4 or 5 samples at different times of 11 animals (n = 47) we calculated delta PDB 13C-medians resulting in small but not significant differences within and significant differences between the species for CO2 and methane. The delta PDB 13C-differences between methane and CO2 were statistically equal within and also between the species. Therefore a linear regression of methane values on CO2 is appropriate and leads to: delta PDB 13C(methane)/1000 = 1.57 * delta PDB 13C(CO2)/1000 - 47/1000 with a correlation coefficient of r = 0.87.  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