全文获取类型
收费全文 | 2810篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 9篇 |
综合类 | 1篇 |
化学工业 | 233篇 |
金属工艺 | 54篇 |
机械仪表 | 15篇 |
建筑科学 | 9篇 |
矿业工程 | 9篇 |
能源动力 | 3篇 |
轻工业 | 17篇 |
水利工程 | 12篇 |
石油天然气 | 40篇 |
无线电 | 61篇 |
一般工业技术 | 263篇 |
冶金工业 | 2017篇 |
原子能技术 | 33篇 |
自动化技术 | 44篇 |
出版年
2022年 | 13篇 |
2021年 | 16篇 |
2020年 | 19篇 |
2019年 | 18篇 |
2018年 | 24篇 |
2017年 | 29篇 |
2016年 | 21篇 |
2015年 | 13篇 |
2014年 | 26篇 |
2013年 | 25篇 |
2012年 | 20篇 |
2011年 | 33篇 |
2010年 | 25篇 |
2009年 | 30篇 |
2008年 | 27篇 |
2007年 | 25篇 |
2006年 | 21篇 |
2005年 | 20篇 |
2004年 | 14篇 |
2003年 | 22篇 |
2002年 | 25篇 |
2001年 | 22篇 |
2000年 | 16篇 |
1999年 | 63篇 |
1998年 | 570篇 |
1997年 | 314篇 |
1996年 | 235篇 |
1995年 | 122篇 |
1994年 | 100篇 |
1993年 | 137篇 |
1992年 | 43篇 |
1991年 | 37篇 |
1990年 | 31篇 |
1989年 | 54篇 |
1988年 | 31篇 |
1987年 | 35篇 |
1986年 | 38篇 |
1985年 | 28篇 |
1984年 | 15篇 |
1982年 | 19篇 |
1981年 | 24篇 |
1980年 | 31篇 |
1979年 | 17篇 |
1978年 | 17篇 |
1977年 | 81篇 |
1976年 | 135篇 |
1975年 | 19篇 |
1974年 | 15篇 |
1972年 | 14篇 |
1968年 | 12篇 |
排序方式: 共有2820条查询结果,搜索用时 15 毫秒
1.
Konstantin V. Dergilev Evgeny K. Shevchenko Zoya I. Tsokolaeva Irina B. Beloglazova Ekaterina S. Zubkova Maria A. Boldyreva Mikhail Yu. Menshikov Elizaveta I. Ratner Dmitry Penkov Yelena V. Parfyonova 《International journal of molecular sciences》2020,21(24)
Cell therapy of the post-infarcted myocardium is still far from clinical use. Poor survival of transplanted cells, insufficient regeneration, and replacement of the damaged tissue limit the potential of currently available cell-based techniques. In this study, we generated a multilayered construct from adipose-derived mesenchymal stromal cells (MSCs) modified to secrete stem cell factor, SCF. In a rat model of myocardium infarction, we show that transplantation of SCF producing cell sheet induced activation of the epicardium and promoted the accumulation of c-kit positive cells in ischemic muscle. Morphometry showed the reduction of infarct size (16%) and a left ventricle expansion index (0.12) in the treatment group compared to controls (24–28%; 0.17–0.32). The ratio of viable myocardium was more than 1.5-fold higher, reaching 49% compared to the control (28%) or unmodified cell sheet group (30%). Finally, by day 30 after myocardium infarction, SCF-producing cell sheet transplantation increased left ventricle ejection fraction from 37% in the control sham-operated group to 53%. Our results suggest that, combining the genetic modification of MSCs and their assembly into a multilayered construct, we can provide prolonged pleiotropic effects to the damaged heart, induce endogenous regenerative processes, and improve cardiac function. 相似文献
2.
3.
Degenerate oligonucleotide primers were used in a polymerase chain reaction (PCR) to amplify a region of the recA sequence of Streptococcus gordonii Challis. The resulting PCR fragment was cloned into the suicide vector pAM6199 and introduced into strain Challis, giving rise to recombination-deficient strains in which the recA gene was specifically inactivated. 相似文献
4.
B. V. Dvoskin D. V. Gulyga A. F. Shevchenko N. T. Tkach N. S. Kharchenko V. P. Shkurenko 《Metallurgist》1989,33(4):68-69
Institute of Ferrous Metallurgy. Translated from Metallurg, No. 4, p. 24, April, 1989. 相似文献
5.
Androstenedione labeled with tritium at positions 1 and 2 was prepared. The molar radioactivity of the sample prepared using homogeneous catalysts was as high as 1.4-1.5 PBq mol-
1. [1,2-3H]Androst-4-ene-3,17-dione can be converted into the [1-3H]steroid with the molar radioactivity of 0.9 PBq mol-
1. 相似文献
6.
M. I. Surin V. E. Keilin S. M. Miklyaev S. A. Shevchenko 《Instruments and Experimental Techniques》2008,51(4):634-637
Within the framework of the “International Thermonuclear Experimental Reactor” (ITER) program, a prototype of a superconducting magnet for a 170-GHz gyrotron has been developed, manufactured, and tested. The operating induction value (7.1 T at the center of a 219-mm-diameter cold hole and 8.1 T on the winding) is reached at a current of 185.2 A. In the final version of the magnet, the required induction value was reached without aging. Special requirements are imposed on the distribution of the magnetic field along the axis, including an abrupt field decrease on both sides of the magnet. Axial forces are additionally taken by a special device. The magnet’s sections are wound with multifiber conductors based on niobium-tin and niobium-titanium alloys. Seventeen resistive shunts are provided for protecting sections during their transition to the normal state. The magnet is equipped with a device for removing a part of energy from the sections. Mechanical stresses in the magnet’s sections and the structure’s power elements have been measured during tests. 相似文献
7.
PJ Jenkins MA Satta M Simmgen WM Drake C Williamson DG Lowe K Britton SL Chew RV Thakker GM Besser 《Canadian Metallurgical Quarterly》1997,47(6):747-751
We report a patient with a metastatic parathyroid carcinoma and medullary carcinoma of the thyroid. This patient represents a variation of the multiple endocrine neoplasia syndrome (MEN) type 2A. There was no evidence of a phaeochromocytoma. The case illustrates the difficulties that may be encountered in localising the source of PTH secretion; the patient underwent four unsuccessful exploratory operations of the neck and mediastinum before further investigations revealed a single metastatic deposit of parathyroid carcinoma involving the first thoracic vertebra. PCR amplification and sequencing of the RET oncogene from the metastatic parathyroid carcinoma and genomic DNA revealed a heterozygous mutation (Cys634Tyr) in exon 11, as has previously been described to occur in MEN 2A. In addition, loss of tumour heterozygosity was demonstrated at loci from chromosomes 1, 2, 3p, 13q and 16p. This represents the first report of a parathyroid carcinoma in a MEN2A patient, in which the multiple allelic deletions are consistent with the generalised losses observed in aggressive tumours. 相似文献
8.
9.
The iron status of 22 children and adolescents with Crohn's disease (mean age: 13 years) was evaluated. Eleven patients were suffering from active disease with inflammation, identified by at least one abnormal value for serum orosomucoid, C-reactive protein or sedimentation rate (group I). Eleven patients were in clinical remission and showed no biological evidence of inflammation (group II). Hemoglobin and red cell indices, erythrocyte protoporphyrin, serum iron, transferrin, serum ferritin and basic red cell ferritin were determined in all patients. The usual indicators of iron status, particularly serum ferritin, were affected by the inflammatory processes, but basic red cell ferritin appeared to be independent of inflammation. Basic red cell ferritin can therefore be considered to be a reliable indicator of iron status in children and adolescents with Crohn's disease. 相似文献
10.
KC Kocis PJ Radell WI Sternberger JE Benson RJ Traystman DG Nichols 《Canadian Metallurgical Quarterly》1997,83(5):1654-1659
Clinically, a noninvasive measure of diaphragm function is needed. The purpose of this study is to determine whether ultrasonography can be used to 1) quantify diaphragm function and 2) identify fatigue in a piglet model. Five piglets were anesthetized with pentobarbital sodium and halothane and studied during the following conditions: 1) baseline (spontaneous breathing); 2) baseline + CO2 [inhaled CO2 to increase arterial PCO2 to 50-60 Torr (6.6-8 kPa)]; 3) fatigue + CO2 (fatigue induced with 30 min of phrenic nerve pacing); and 4) recovery + CO2 (recovery after 1 h of mechanical ventilation). Ultrasound measurements of the posterior diaphragm were made (inspiratory mean velocity) in the transverse plane. Images were obtained from the midline, just inferior to the xiphoid process, and perpendicular to the abdomen. M-mode measures were made of the right posterior hemidiaphragm in the plane just lateral to the inferior vena cava. Abdominal and esophageal pressures were measured and transdiaphragmatic pressure (Pdi) was calculated during spontaneous (Sp) and paced (Pace) breaths. Arterial blood gases were also measured. Pdi(Sp) and Pdi(Pace) during baseline + CO2 were 8 +/- 0.7 and 49 +/- 11 cmH2O, respectively, and decreased to 6 +/- 1.0 and 27 +/- 7 cmH2O, respectively, during fatigue + CO2. Mean inspiratory velocity also decreased from 13 +/- 2 to 8 +/- 1 cm/s during these conditions. All variables returned to baseline during recovery + CO2. Ultrasonography can be used to quantify diaphragm function and identify piglet diaphragm fatigue. 相似文献