全文获取类型
收费全文 | 3739篇 |
免费 | 5篇 |
专业分类
电工技术 | 1篇 |
综合类 | 1篇 |
化学工业 | 31篇 |
金属工艺 | 6篇 |
机械仪表 | 1篇 |
建筑科学 | 6篇 |
能源动力 | 1篇 |
轻工业 | 21篇 |
石油天然气 | 1篇 |
无线电 | 6篇 |
一般工业技术 | 17篇 |
冶金工业 | 3618篇 |
自动化技术 | 34篇 |
出版年
2021年 | 2篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 7篇 |
2015年 | 1篇 |
2014年 | 8篇 |
2013年 | 5篇 |
2012年 | 8篇 |
2011年 | 5篇 |
2010年 | 6篇 |
2009年 | 8篇 |
2008年 | 6篇 |
2007年 | 3篇 |
2006年 | 4篇 |
2005年 | 8篇 |
2004年 | 2篇 |
2003年 | 13篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 129篇 |
1998年 | 1246篇 |
1997年 | 674篇 |
1996年 | 400篇 |
1995年 | 244篇 |
1994年 | 190篇 |
1993年 | 241篇 |
1992年 | 34篇 |
1991年 | 47篇 |
1990年 | 41篇 |
1989年 | 31篇 |
1988年 | 25篇 |
1987年 | 42篇 |
1986年 | 24篇 |
1985年 | 24篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 65篇 |
1976年 | 113篇 |
1975年 | 3篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1955年 | 1篇 |
1930年 | 2篇 |
1904年 | 2篇 |
1901年 | 1篇 |
排序方式: 共有3744条查询结果,搜索用时 15 毫秒
71.
SJ Phillips 《Canadian Metallurgical Quarterly》1993,55(5):1281-1282
72.
American Academy of Pediatrics (AAP) fellows responded to a questionnaire measuring knowledge of 1991 Centers for Disease Control and Prevention (CDC) guidelines. Generalists' scores on a knowledge scale were positively correlated with reporting CDC and AAP documents as knowledge sources, and negatively correlated with private practice, medical school as a knowledge source, and age. However, private practitioners who read AAP documents scored well. 相似文献
73.
74.
75.
Real-time ultrasonic measurements of 10th-rib backfat (BF10) and loin muscle area (LMA) were made by a single technician at four mean BW (67.4, 80.3, 93.4, and 104.9 kg) on live hogs to assess the accuracy of predicting carcass measurements before and at slaughter weight. Records were evaluated on 655 purebred barrows and 472 purebred gilts in two tests. Residual correlations-accounting for test, sex, and breed effects, among and between scans and carcass measurements--were moderate to high for BF10 (r=.69 to .82) and LMA (r=.57 to .68), with the largest correlations at 104.9 kg of live weight. Ultrasonic BF10 and LMA were within +/-4 mm and +/-6.45 cm2, respectively, of the corresponding carcass measurement 75.9 and 89.8% of the time. Sex differences for LMA bias were significant (P < .001); ultrasonic LMA was overestimated in barrows by .75 cm2 and underestimated in gilts by .91 cm2. Breed differences were significant (P < .001) for BF10 and LMA bias. Standard errors of prediction (SEP) for BF10 and LMA across the two tests were 3.46 mm and 4.04 cm2, respectively. The SEP for BF10 were 3.60 mm for barrows and 3.19 mm for gilts. The SEP for LMA were 3.77 cm2 for barrows and 4.22 cm2 for gilts. The SEP for BF10 within breeds ranged from 3.25 to 3.72 mm, and for LMA, ranged from 2.98 cm2 to 4.90 cm2. Ultrasound measurements overestimated the carcass measurement by .57 mm for carcasses measuring < 24.1 mm and underestimated by 2.81 mm carcasses with BF10 > 30.3 mm. Ultrasonic LMA overestimated the carcass by 2.35 cm2 in carcasses measuring < 32.5 cm2 and underestimated by 2.29 cm2 in carcasses measuring greater than 37.9 cm2. Results indicate that the magnitude of the carcass measurement affects bias and accuracy of prediction for real-time ultrasonic measurements of BF10 and LMA. The SEP statistic is more consistent in evaluating accuracy of ultrasonic measurement than bias, absolute deviations, and percentage of absolute deviation. 相似文献
76.
The mechanism of decline in viremia following acute infection with HIV is unknown. To characterize this process virologically, the expression of viral RNAs was analyzed in samples of peripheral blood mononuclear cells (PBMCs) from a patient who experienced a 100-fold decline in plasma viremia over a 13-day period prior to the initiation of antiretroviral therapy. Cell-associated viral RNA declined in association with the decline in plasma virus. During the initial 7 days of observation, plasma viremia declined more than 10-fold with no change in the ratio of unspliced to multiply spliced mRNAs. The efficiency of viral gene expression did not decline during the study period and varied from 380 to 2800 unspliced RNA copies per productively infected cell. Together, these data indicate no change in the relative proportion of cells in late- and early-stage gene expression during the initial decline and provide evidence against shortening of the viral replication cycle by immune surveillance. However, the prevalence of productively infected cells declined markedly during the 13 days of observation, from 1 in 250 to 1 in 25,000 PBMCs. These data are compatible with depletion of available target cells during the initial decline in viremia. As the level of plasma virus stabilized after 8 days of observation, the ratio of unspliced to multiply spliced mRNAs rose; this rise was due to a relatively greater decline in multiply spliced mRNA. These data suggest the possible onset of a blockade to new infection events (for example, by neutralizing antibody or chemokines), causing an increase in the relative proportion of cells in late-stage gene expression. They may also be explained, however, by the persistence of cell-associated virions together with the near disappearance of productively infected cells from the circulation. 相似文献
77.
Prothrombin and thrombin are involved in diverse biological functions. The structure of prothrombin has been studied extensively and its cDNA has been cloned from several species. The tissue-specific expression of this protein has been studied, as well as the developmental expression pattern. The structure of the human gene coding for prothrombin has been determined, and gene regulation studies have been performed that indicate that HNF-1 might be responsible for the liver-specific expression of this protein. Other regulatory elements have been identified. In order to further study the biological properties of prothrombin, prothrombin-deficient mice have been generated using gene targeting technology. Prothrombin deficiency in mice results in partial embryonic lethality. The mice that survive to birth die from bleeding events. The embryonic lethality occurs between embryonic days 9.5 and 11.5 and appears to be due to the loss of integrity of the vasculature due to a failure in blood coagulation. These results indicate that prothrombin plays not only a key role in hemostasis but suggests that it may be important for mouse development. 相似文献
78.
D Kahn RD Williams MK Haseman NL Reed SJ Miller J Gerstbrein 《Canadian Metallurgical Quarterly》1998,16(1):284-289
PURPOSE: We investigated the ability of In-111-capromab pendetide to separate patients who have failed radical prostatectomy into categories of those who would versus those who would not respond to salvage radiotherapy. METHODS: Prostate-specific antigen (PSA) levels in 32 men with prostate cancer who had failed radical prostatectomy and had undergone a whole-body In-111-capromab pendetide scan were followed-up for 13 months (median) after salvage radiotherapy to the pelvis. A logistic regression model was used to determine whether the scan findings, as well as other clinical variables, were associated with a durable complete response (DCR), a nondurable response (NDR), or no response (NR). RESULTS: Sixteen of 23 (70%) men with a normal scan outside the prostatic fossa achieved a DCR after salvage radiotherapy versus two of nine (22%) who had a positive scan outside the prostate fossa and pelvis (P = .0225, Fisher's exact test). Predicted probability (95% confidence interval [CI]) that a DCR would be obtained with a normal scan was 0.88 (0.55 to 0.98); for men with a positive scan limited to the prostatic fossa it was 0.62 (0.42 to 0.79); and for men with a positive scan outside the pelvis it was 0.27 (0.09 to 0.58). No other variables before radiotherapy showed a significant association with the DCR rate. CONCLUSION: Salvage radiotherapy is statistically more likely to lead to a durable complete PSA response in men with prostate cancer who have failed radical prostatectomy and have a negative In-111-capromab pendetide scan outside the pelvis as compared with those who have a positive scan. 相似文献
79.
DK Robbins MA Castles DJ Pack VO Bhargava SJ Weir 《Canadian Metallurgical Quarterly》1998,19(7):455-463
The pharmacokinetics and dose proportionality of fexofenadine, a new non-sedating antihistamine, and its enantiomers were characterized after single and multiple-dose administration of its hydrochloride salt. A total of 24 healthy male volunteers (31 +/- 8 years) received oral doses of 20, 60, 120 and 240 mg fexofenadine HCl in a randomized, complete four-period cross-over design. Subjects received a single oral dose on day 1, and multiple oral doses every 12 h on day 3 through the morning on day 7. Treatments were separated by a 14-day washout period. Serial blood and urine samples were collected for up to 48 h following the first and last doses of fexofenadine HCl. Fexofenadine and its R(+) and S(-) enantiomers were analysed in plasma and urine by validated HPLC methods. Fexofenadine pharmacokinetics were linear across the 20-120 mg dose range, but a small disproportionate increase in area under the plasma concentration-time curve (AUC) (< 25%) was observed following the 240 mg dose. Single-dose pharmacokinetics of fexofenadine were predictive of steady-state pharmacokinetics. Urinary elimination of fexofenadine played a minor role (10%) in the disposition of this drug. A 63:37 steady-state ratio of R(+) and S(-) fexofenadine was observed in plasma. This ratio was essentially constant across time and dose. R(+) and S(-) fexofenadine were eliminated into urine in equal rates and quantities. All doses of fexofenadine HCl were well tolerated after single and multiple-dose administration. 相似文献
80.
SJ Ander LM Blomkvist JC M?lne KJ Johansson SP Smeds 《Canadian Metallurgical Quarterly》1997,20(11):640-647
The morphology, cell proliferation and function of transplanted normal, hyperplastic and adenomatous human parathyroid tissue was studied after transplantation to athymic mice. The iPTH was evaluated in relation to morphology. Human parathyroid tissue collected during surgery for hyperparathyroidism was implanted subcutaneously into athymic mice (nu/nu-BALB/cA) and was analysed 1, 4, 7 and 12 weeks after transplantation. The transplants were examined by light and electron microscopy and by autoradiography after continuous infusion of 3H-thymidine. The relative amount of viable tissue was evaluated using a computer image analysing programme. Graft function was evaluated by measuring human iPTH in mouse serum. A transplant take ratio of 93% was observed. The proliferation rate in adenoma grafts at 12 weeks after transplantation was five and fifteen times that observed in normal and hyperplastic transplants, respectively. In normal and adenoma groups, a continuous increase in iPTH concentrations was observed, but in the hyperplastic group the iPTH remained on the same level. The secretion of iPTH in relation to the amount of transplanted tissue and the fraction of viable tissue was at the same level at 12 weeks in normal and adenomatous grafted animals. In conclusion, human parathyroid tissue was successfully transplanted and maintained its original structure. The growth potential, but not the iPTH secretion, was significantly higher in adenoma grafts compared to grafts from hyperplastic and normal glands. 相似文献