全文获取类型
收费全文 | 2337篇 |
免费 | 39篇 |
专业分类
电工技术 | 15篇 |
综合类 | 2篇 |
化学工业 | 214篇 |
金属工艺 | 37篇 |
机械仪表 | 19篇 |
建筑科学 | 55篇 |
能源动力 | 34篇 |
轻工业 | 99篇 |
水利工程 | 11篇 |
无线电 | 116篇 |
一般工业技术 | 223篇 |
冶金工业 | 1390篇 |
原子能技术 | 16篇 |
自动化技术 | 145篇 |
出版年
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 16篇 |
2020年 | 11篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2017年 | 18篇 |
2016年 | 25篇 |
2015年 | 23篇 |
2014年 | 21篇 |
2013年 | 48篇 |
2012年 | 42篇 |
2011年 | 56篇 |
2010年 | 41篇 |
2009年 | 34篇 |
2008年 | 46篇 |
2007年 | 50篇 |
2006年 | 35篇 |
2005年 | 39篇 |
2004年 | 39篇 |
2003年 | 35篇 |
2002年 | 35篇 |
2001年 | 34篇 |
2000年 | 27篇 |
1999年 | 57篇 |
1998年 | 370篇 |
1997年 | 239篇 |
1996年 | 158篇 |
1995年 | 100篇 |
1994年 | 89篇 |
1993年 | 115篇 |
1992年 | 24篇 |
1991年 | 20篇 |
1990年 | 38篇 |
1989年 | 35篇 |
1988年 | 31篇 |
1987年 | 32篇 |
1986年 | 22篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 16篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1977年 | 31篇 |
1976年 | 73篇 |
1975年 | 16篇 |
1974年 | 10篇 |
1972年 | 8篇 |
排序方式: 共有2376条查询结果,搜索用时 0 毫秒
991.
This study examined the effects of an individualized computerized testing system for baccalaureate nursing students enrolled in health assessment and obstetrics/women's health during a 3-year period. One hundred twenty-seven students participated in the study. The testing software, Pedagogue, was used to generate the computer tests, and the students took all quizzes on-line. The mean scores on computer tests in both courses were as good as, or better than, previous scores on paper-pencil forms of the tests (P < .05). 相似文献
992.
KC Ong H Wen AS Chesnick S Duewell FA Jaffer RS Balaban 《Canadian Metallurgical Quarterly》1995,5(6):773-777
Because radiation loss associated with a radiofrequency (RF) coil increases as roughly the fourth power of the frequency, this loss mechanism may become important in high-field studies above 2.0 T. In this study, the contribution of radiation losses at 4.0 T were determined in a rectangular surface coil using an RF shield to modify the radiation losses. The effect of this shield was determined on coil Q, B1 distribution, and signal to noise as a function of distance between the coil and the shield. Phantoms and human tissue were evaluated to characterize the loss mechanisms. The results demonstrate a large radiation loss in the unshielded surface coil. However, the radiation losses in vivo were not dominant owing to a large inductive loss occurring from dielectric currents in the body at 170 MHz. 相似文献
993.
994.
OBJECTIVES: This paper describes national trends in mortality of children with sickle cell disease and the settings in which death occurred. METHODS: United States death certificate data from 1968 through 1992 were used to calculate mortality rates of Black children with sickle cell disease 1 to 14 years old. Deaths from trauma, congenital anomalies, and perinatal conditions were excluded. RESULTS: Between 1968 and 1992, mortality rates of Black children with sickle cell disease decreased 41% for 1- to 4-year-olds, 47% for 5- to 9-year-olds, and 53% for 10- to 14-year-olds. During 1986 through 1992, children who died before hospital admission accounted for 41% of deaths among 1- to 4-year-olds, 27% among 5- to 9-year-olds, and 12% among 10- to 14-year-olds. CONCLUSIONS: Survival of Black children with sickle cell disease has improved markedly since 1968. A substantial proportion of deaths continue to occur prior to hospital admission. Trends in sickle cell mortality can be monitored inexpensively with death-certificate data. 相似文献
995.
KC McCourt L Salmela RK Mirakhur M Carroll MT M?kinen M Kansanaho C Kerr GJ Roest KT Olkkola 《Canadian Metallurgical Quarterly》1998,53(9):867-871
Past investigations of in vivo arterial behavior have concentrated on determining material properties based upon the maximum and minimum pressure and diameter measured over a pulse cycle. A new in vivo technique, based upon continuous measurement of pressure and flow, has been developed to study arterial compliance throughout the pulse cycle. Compliance in the abdominal aorta of rats showed different behavior during the rising and falling portion of the pressure pulse. Previous investigations of canine arteries which used different methods are consistent with these findings. This study demonstrates the utility of a new measurement technique and shows some trends in compliance within the pulse cycle which have neither been revealed by static tests nor by dynamic tests which focused on pulse averaged values. 相似文献
996.
KC Parker JI Garrels W Hines EM Butler AH McKee D Patterson S Martin 《Canadian Metallurgical Quarterly》1998,19(11):1920-1932
With the complete sequence of the yeast genome now available, efforts by many laboratories are underway to identify each of the spots on two-dimensional (2-D) gels corresponding to the most abundant yeast proteins. The high mass accuracy now attainable using matrix assisted laser desorption/ionization (MALDI)-mass spectrometry equipped with delayed extraction simplifies the process of identification, such that many spots can be unambiguously identified in a short period of time merely by using peptide mass fingerprinting and generally available database matching programs. Although it is not always possible to match spots between gels run by different laboratories, proteins generally yield the same abundant proteolytic fragments when tryptic digestions are performed. Databases containing these signature peptides not only simplify the task of reidentifying proteins from different gels, but also make it possible to identify small amounts of cross-contaminating proteins from different spots, as well as common extraneous contaminants such as human keratins. In this paper, we present data on the identification of > 20 previously unreported yeast proteins from 2-D gels. Some novel proteins were identified from randomly analyzed spots. Focusing on 14 spots in a narrow-pH-range gel, we demonstrate how organizing peak-table data and peptide match-list data into databases enables the identification of a larger percentage of the peaks. 相似文献
997.
C Sinderby J Beck J Spahija J Weinberg A Grassino 《Canadian Metallurgical Quarterly》1998,85(6):2146-2158
Intersubject comparison of the crural diaphragm electromyogram, as measured by an esophageal electrode, requires a reliable means for normalizing the signal. The present study set out 1) to evaluate which voluntary respiratory maneuvers provide high and reproducible diaphragm electromyogram root-mean-square (RMS) values and 2) to determine the relative diaphragm activation and mechanical and ventilatory outputs during breathing at rest in healthy subjects (n = 5), in patients with severe chronic obstructive pulmonary disease (COPD, n = 5), and in restrictive patients with prior polio infection (PPI, n = 6). In all groups, mean voluntary maximal RMS values were higher during inspiration to total lung capacity than during sniff inhalation through the nose (P = 0.035, ANOVA). The RMS (percentage of voluntary maximal RMS) during quiet breathing was 8% in healthy subjects, 43% in COPD patients, and 45% in PPI patients. Despite the large difference in relative RMS (P = 0.012), there were no differences in mean transdiaphragmatic pressure (P = 0.977) and tidal volumes (P = 0.426). We conclude that voluntary maximal RMS is reliably obtained during an inspiration to total lung capacity but a sniff inhalation could be a useful complementary maneuver. Severe COPD and PPI patients breathing at rest are characterized by increased diaphragm activation with no change in diaphragm pressure generation. 相似文献
998.
999.
JW Simons EM Jaffee CE Weber HI Levitsky WG Nelson MA Carducci AJ Lazenby LK Cohen CC Finn SM Clift KM Hauda LA Beck KM Leiferman AH Owens S Piantadosi G Dranoff RC Mulligan DM Pardoll FF Marshall 《Canadian Metallurgical Quarterly》1997,57(8):1537-1546
Granulocyte-macrophage colony-stimulating factor (GM-CSF) gene-transduced, irradiated tumor vaccines induce potent, T-cell-mediated antitumor immune responses in preclinical models. We report the initial results of a Phase I trial evaluating this strategy for safety and the induction of immune responses in patients with metastatic renal cell carcinoma (RCC). Patients were treated in a randomized, double-blind dose-escalation study with equivalent doses of autologous, irradiated RCC vaccine cells with or without ex vivo human GM-CSF gene transfer. The replication-defective retroviral vector MFG was used for GM-CSF gene transfer. No dose-limiting toxicities were encountered in 16 fully evaluable patients. GM-CSF gene-transduced vaccines were equivalent in toxicity to nontransduced vaccines up to the feasible limits of autologous tumor vaccine yield. No evidence of autoimmune disease was observed. Biopsies of intradermal sites of injection with GM-CSF gene-transduced vaccines contained distinctive macrophage, dendritic cell, eosinophil, neutrophil, and T-cell infiltrates similar to those observed in preclinical models of efficacy. Histological analysis of delayed-type hypersensitivity responses in patients vaccinated with GM-CSF-transduced vaccines demonstrated an intense eosinophil infiltrate that was not observed in patients who received nontransduced vaccines. An objective partial response was observed in a patient treated with GM-CSF gene-transduced vaccine who displayed the largest delayed-type hypersensitivity conversion. No replication-competent retrovirus was detected in vaccinated patients. This Phase I study demonstrated the feasibility, safety, and bioactivity of an autologous GM-CSF gene-transduced tumor vaccine for RCC patients. 相似文献
1000.