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   3458篇
  免费   8篇
  国内免费   1篇
电工技术   2篇
综合类   3篇
化学工业   23篇
金属工艺   3篇
机械仪表   2篇
建筑科学   9篇
矿业工程   1篇
能源动力   3篇
轻工业   10篇
石油天然气   1篇
武器工业   2篇
无线电   10篇
一般工业技术   8篇
冶金工业   3374篇
自动化技术   16篇
  2022年   2篇
  2021年   1篇
  2020年   1篇
  2017年   2篇
  2016年   2篇
  2014年   1篇
  2013年   6篇
  2012年   1篇
  2011年   26篇
  2010年   5篇
  2009年   2篇
  2008年   2篇
  2006年   1篇
  2005年   4篇
  2004年   5篇
  2003年   9篇
  2002年   3篇
  2000年   3篇
  1999年   118篇
  1998年   1125篇
  1997年   653篇
  1996年   389篇
  1995年   194篇
  1994年   178篇
  1993年   228篇
  1992年   13篇
  1991年   28篇
  1990年   27篇
  1989年   41篇
  1988年   33篇
  1987年   33篇
  1986年   16篇
  1985年   25篇
  1984年   1篇
  1983年   7篇
  1982年   17篇
  1981年   13篇
  1980年   26篇
  1979年   1篇
  1978年   10篇
  1977年   75篇
  1976年   136篇
  1971年   1篇
  1955年   3篇
排序方式: 共有3467条查询结果,搜索用时 406 毫秒
171.
Human calicivirus Sapporo (SV) has typical calicivirus morphology and causes acute gastroenteritis in children. The nucleotide sequence of 3.2 kb of the 3' end of SV was determined from a cloned cDNA. The 3' end of the SV genome is predicted to encode the RNA-dependent RNA polymerase region, the capsid protein and two small open reading frames. The nonstructural and capsid protein coding sequences in the SV genome are fused in a single open reading frame. The organization of these proteins in the SV sequence is similar to that of rabbit hemorrhagic disease virus and the recently described Manchester virus, and distinct from the genome organization of the prototype human calicivirus, Norwalk virus, that lacks typical calicivirus morphology and has been described as a small round structured virus (SRSV). Sequence analysis of the predicted capsid region showed that the SV capsid is longer by approximately 30 amino acids than the capsid of any of the SRSVs, and multiple sequence alignments showed that these additional amino acids are located in the variable region of the capsid protein. Expression of the capsid protein of SV in insect cells resulted in the self-assembly of virus-like particles that have a morphology similar to that of the native virus. This result shows that calicivirus morphology is determined by the primary sequence of the capsid protein.  相似文献   
172.
BACKGROUND: The authors previously reported a statistically significant effect of psychosocial intervention on survival time of women with metastatic breast carcinoma. In this study, the authors investigated whether this effect could be explained by differences in the medical treatment patients received subsequent to their group participation or differences in causes of death. METHODS: Of the original 86 study participants, medical treatment charts for 61 and death certificates for 83 were available for further analysis. The authors reviewed the course of the medical treatment they received subsequent to their entry into the randomized psychotherapy trial. RESULTS: Although there were no statistically significant differences with regard to chemotherapy and hormone therapy between the control and treatment groups, women in the control group tended to have received more adrenalectomies, although this procedure did not account for the difference in survival time between the control group and the treatment group. Furthermore, women in the control group developed more bone and lung metastases than the women in the treatment group. CONCLUSIONS: Differences in disease course between the control and treatment groups appeared to be independent of any differences in medical treatment received.  相似文献   
173.
174.
We investigated the utility of two approaches for exploiting pleiotropy to search for genes influencing related traits. To do this we first assessed the genetic correlations among a set of five closely related quantitative traits (Q1, Q2, Q3, Q4, Q5). We then used the genetic correlations among these five traits both to remove the common genetic effects of the four remaining traits, thereby identifying the unique genetic contribution to each trait, and to extract a synthetic phenotype which exploits the shared genetic information (pleiotropy) among these five traits. After obtaining these conditional traits, we then searched for evidence of quantitative trait loci (QTLs) (using variance component linkage) influencing the unique residual genetic component for each trait as well as those influencing the expression of the synthetic traits. From this work, we conclude that the removal of the common genetic effects of other traits in a group may be of greater utility when the majority of the pleiotropy initially detected between traits is attributable to the shared additive effects of polygenes, rather than to those of major loci. By contrast, decomposition of the genetic covariance matrix to its principal components is a greater utility when the majority of pleiotropy is attributable to major loci.  相似文献   
175.
BACKGROUND: Adynamic bone disease (ABD) has been described in the current dialysis population to have an unexpectedly high prevalence. Moreover, it is clearly more prevalent in CAPD patients, compared to haemodialysis patients. Recently we demonstrated that both a low (< or = 27 U/1) level of bone alkaline phosphatase (BAP) as determined by an optimized agarose gel electrophoretic technique and a low (< or = 150 pg/ml ) level of iPTH are good markers of ABD with sensitivities of 78.1% and 80.6% and specificities of 86.4% and 76.2% respectively. METHODS: In this study (n = 212), the prevalence of ABD in the European CAPD population was evaluated by means of these biochemical markers. Clinical data on the patients included were recorded at the moment of blood sampling. In patients under CAPD treatment for longer than 9 months, we calculated an index of calcium exposure through PD fluid. RESULTS: In this population with a low exposure to aluminium, the prevalence of ABD as indicated by either a low level of BAP or PTH was 43%. The following risk factors could be identified: advanced age, shorter time on renal replacement therapy, male gender, and high calcium content of PD fluid. The index of calcium exposure was significantly higher in the patients with low BAP and low iPTH levels compared to those with either BAP > or = 27 U/1 or iPTH > 150 pg/ml. The latter finding gives further support to the hypothesis that a high calcium load administered to renal failure patients may lead to 'oversuppressed' parathyroids in ABD. In a subgroup of patients with a high level of BAP associated with a low iPTH level a profile previously shown to be associated in the presence of aluminium overload, significantly higher serum aluminium levels were noted. suggesting that even in patients with low exposure to aluminium, this element still can affect bone metabolism. CONCLUSION: A high prevalence of ABD--as diagnosed by biochemical markers--was observed in the European CAPD population. A number of risk factors could be put forward. The aetiology and pathogenesis of this type of renal osteodystrophy remain to be elucidated, but appear, however, to be multifactorial.  相似文献   
176.
S Teich  DP Barton  ME Ginn-Pease  DR King 《Canadian Metallurgical Quarterly》1997,32(7):1075-9; discussion 1079-80
Since 1962, the Waterston classification has been used to stratify neonates who have esophageal atresia (EA) and/or tracheoesophageal fistula (TEF) into prognostic categories based on birth weight, the presence of pneumonia, and the identification of other congenital anomalies. In response to advances in neonatal care, the surgeons from the Montreal Children's Hospital proposed a new categorization system in 1993 in an attempt to define the current risk factors for patients who have EA/TEF. In the Montreal experience only two characteristics independently affected survival: preoperative ventilator dependence and associated major anomalies. The goal of this study was to determine which system had the greatest validity for the evaluation of prognosis in our patients with EA/TEF. The charts of 94 patients who had EA/TEF treated between 1972 and 1991 were reviewed. Patients were classified using both the Waterston and Montreal systems. Groups were compared with Fisher's Exact test using a 95% confidence level for statistical significance. Eleven infants were ventilator dependent preoperatively; 62 children had major associated anomalies, 8 of which were considered life threatening. Sixteen children died within 4 years, eight during their initial hospital stay. Five of the eight early postoperative deaths occurred in the highest-risk patients (Waterston C or Montreal II). Analysis was performed for multiple risk factors and mortality. As in the Montreal study, the presence of life-threatening and major congenital anomalies represented significant risk factors for death. Pulmonary disease as delineated by ventilator dependence appeared to be more accurate than pneumonia. This study confirms the accuracy of the Montreal classification in defining prognosis for EA/TEF. The Montreal system more accurately identifies children at highest risk than the Waterston classification.  相似文献   
177.
178.
Although body condition score was not significantly different between light (<55 kg, n = 6) and heavy (> or =60 kg, n = 7) ewes at mating, it declined between Day 30 and Day 90 of gestation in light but not heavy ewes, and remained lower up to term. All ewes bore twins, delivered near term (Days 144-146) by Caesarean section. One lamb was immediately placed into a warm (30 degrees C; WD) and its twin into a cool (15 degrees C; CD) ambient temperature, and tissues were sampled at 0.5 h or 6 h. All CD lambs born to light ewes exhibited hypothermia and/or respiratory failure and did not survive longer than 30 min; these symptoms were not observed in their WD twins or any lamb born to heavy ewes. Total lamb birth weight, placental weight and fetal cotyledonary weight were lower with light than with heavy ewes. Lambs born to light ewes had less perirenal adipose tissue and smaller liver, heart, kidneys, brain, adrenals and thyroid, although their heart, brain and pancreas represented a larger proportion of total bodyweight; pancreas weight was similar to that in lambs born to heavy ewes. Hence, maternal bodyweight critically influences placental weight and lamb size and survival after birth.  相似文献   
179.
The effect of the cyclin-dependent (CDK) inhibitors olomoucine and roscovitine on cell kinetics was studied. To this end, nonsmall cell lung cancer (NSCLC) cell line MR65 and neuroblastoma cell line CHP-212 were pulse labeled with bromodeoxyuridine (BrdUrd) and chased in culture medium, to which various concentrations of olomoucine or roscovitine were added. A dose-dependent inhibition of the G1/S-phase and G2/ M-/G1 transitions was observed. Furthermore, S-phase progression was also inhibited in a dose-dependent manner. Similarly, roscovitine, another CDK inhibitor with a 10-fold higher efficiency for both CDK1 and CDK2 as compared to olomoucine, showed the same effects at a 10-fold lower concentration. At the highest tested doses both olomoucine (200 microM) and roscovitine (40 microM) induced a complete cell cycle block in both cell lines, paralleled by the appearance of apoptotic figures. In these cultures a decrease in CDK1 protein level was found as shown by Western blotting. Bivariate CDK1/DNA analysis confirmed these observations and showed that a subpopulation of cells with characteristics of apoptosis became CDK1 negative. The presented data suggest that cyclins and CDKs are involved at an important nodal point shared by pathways regulating cellular proliferation and apoptosis.  相似文献   
180.
OBJECTIVES: Our objectives were to (1) expand and strengthen the women's health curriculum at the University of California, San Francisco, and (2) evaluate the responses of both medical students and faculty to this curriculum. STUDY DESIGN: A written evaluation of the curriculum in women's health was completed by both students and faculty. Variables studied included mean scores of cases, the overall course score, and the preferences of medical students for faculty specialty in teaching the small groups. RESULTS: The overall course evaluation score was 7.81 (range 1 to 10). For those students who had both faculty from internal medicine or family medicine and obstetrics and gynecology, there was a strong preference that obstetrician-gynecologists teach the majority of the cases. CONCLUSIONS: The new case-based curriculum in women's health was enthusiastically received by both medical students and faculty.  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