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   5124篇
  免费   102篇
  国内免费   19篇
电工技术   262篇
综合类   7篇
化学工业   933篇
金属工艺   154篇
机械仪表   98篇
建筑科学   72篇
矿业工程   2篇
能源动力   106篇
轻工业   279篇
水利工程   8篇
石油天然气   17篇
无线电   551篇
一般工业技术   1011篇
冶金工业   1285篇
原子能技术   160篇
自动化技术   300篇
  2023年   14篇
  2021年   96篇
  2020年   37篇
  2019年   56篇
  2018年   59篇
  2017年   59篇
  2016年   75篇
  2015年   55篇
  2014年   83篇
  2013年   180篇
  2012年   167篇
  2011年   233篇
  2010年   157篇
  2009年   160篇
  2008年   171篇
  2007年   183篇
  2006年   153篇
  2005年   156篇
  2004年   139篇
  2003年   137篇
  2002年   105篇
  2001年   105篇
  2000年   104篇
  1999年   134篇
  1998年   536篇
  1997年   288篇
  1996年   212篇
  1995年   164篇
  1994年   128篇
  1993年   117篇
  1992年   78篇
  1991年   80篇
  1990年   62篇
  1989年   69篇
  1988年   50篇
  1987年   55篇
  1986年   60篇
  1985年   58篇
  1984年   54篇
  1983年   37篇
  1982年   42篇
  1981年   46篇
  1980年   41篇
  1979年   30篇
  1978年   29篇
  1977年   28篇
  1976年   73篇
  1975年   17篇
  1974年   14篇
  1973年   13篇
排序方式: 共有5245条查询结果,搜索用时 531 毫秒
81.
We developed a method that allows prenatal diagnosis of Duchenne muscular dystrophy using a single nucleated erythrocyte (NRBC) isolated from maternal blood. Maternal blood was obtained at 8 to 20 weeks of gestation. NRBCs were separated with Percoll using a discontinuous density gradient method and then collected by micromanipulator under microscopic observation. The entire genome of a single cell amplified by primer extension preamplification (PEP). Sex was determined from a small aliquot of the PEP reaction. After an NRBC was determined to be male and confirmed to be of fetal origin, dystrophin exons 4, 8, 12, 45, 48, 50, and 51 were determined from the same PEP reaction. This diagnostic method using maternal blood is safer than amniocentesis or cordocentesis and can be applied to other X-linked disease.  相似文献   
82.
The WF (wall failure) test of the EAGLE program, in which 2 kg of uranium dioxide fuel-pins were melted by nuclear heating, was successfully conducted in the IGR (Impulse Graphite Reactor) of NNC/Kazakhstan. In this test, a 3 mm-thick stainless steel (SS) wall structure was placed between fuel pins and a 10 mm-thick sodium-filled channel (sodium gap). During the transient, fuel pins were heated, which led to the formation of a fuel-steel mixture pool. Under the transient nuclear heating condition, the SS wall was strongly heated by the molten pool, leading to wall failure. The time needed for fuel penetration into the sodium-filled gap was very short (less than 1 s after the pool formation). The result suggests that molten core materials formed in hypothetical LMFBR core disruptive accidents have a certain potential to destroy SS-wall boundaries early in the accident phase, thereby providing fuel escape paths from the core region. The early establishment of such fuel escape paths is regarded as a favorable characteristic in eliminating the possibility of severe re-criticality events. A preliminary interpretation on the WF test results is presented in this paper.  相似文献   
83.
A clean benchmark experiment on beryllium was performed with D-T neutrons at the FNS facility of the Japan Atomic Energy Agency. The main objective was to verify the integral data related to the tritium production on lithium isotopes. Tritium production rates, as well as activation reaction rates were measured inside the beryllium assembly that was shaped as a pseudo-cylindrical slab with an area-equivalent diameter of 628 mm and a thickness of 355 mm. Experimental results were analyzed with a three-dimensional Monte Carlo transport code MCNP-4C and FENDL/MC-2.0, JENDL-3.2/3.3 neutron transport libraries. Evaluation of reaction rates was based on the cross section data taken from the JENDL Dosimetry File and ENDF B-VI data libraries. Analysis shows that all calculation combinations (transport and activation cross section libraries) used for evaluation of reaction rates give data that is agreeable with measured values within 10%.  相似文献   
84.
A new triazol antifungal agent, (+)-2-(2,4-difluorophenyl)-3-methyl-1-(1H-1, 2,4-triazol-1-yl)-3-[6-(1H-1,2,4-triazol-1-yl)pyridazin++ +-3-ylthio]butan-2-ol (MFB-1041), shows poor oral absorption and is practically insoluble in water (1.2 micrograms/ml). Solid dispersion systems with an enteric polymer such as hydroxypropylmethylcellulose phthalate (HP-55) and carboxymethylethylcellulose (CMEC), and a nonenteric polymer, hydroxypropylmethylcellulose (Metolose) were evaluated to improve drug absorption and solubility. The oral bioavailabilities of these solid dispersions in beagle dogs were over 6 times higher than that of a suspension system with increasing drug solubility in an alkaline medium. X-Ray powder diffraction measurement of the solid dispersion showed a complete drug phase change from a crystal to an amorphous state. Further, from the results of a stability test, the preparations were stable in a desiccated condition and the absorption profiles also showed no change. From the results, it was suggested that the oral administrative preparation of MFB-1041 having a superior absorption profile and a high stability could be obtained by a drug phase change from a crystal to an amorphous state, especially in the spray-drying method using enteric polymers.  相似文献   
85.
A spherical acoustic resonator was developed for measuring sound velocities in the gaseous phase and ideal-gas specific heats for new refrigerants. The radius of the spherical resonator, being about 5 cm, was determined by measuring sound velocities in gaseous argon at temperatures from 273 to 348 K and pressures up to 240 kPa. The measurements of 23 sound velocities in gaseous HFC-134a (1,1,1,2-tetrafluoroethane) at temperatures of 273 and 298 K and pressures from 10 to 250 kPa agree well with the measurements of Goodwin and Moldover. In addition, 92 sound velocities in gaseous HFC-152a (1,1-difluoroethane) with an accuracy of ±0.01% were measured at temperatures from 273 to 348 K and pressures up to 250 kPa. The ideal-gas specific heats as well as the second acoustic virial coefficients have been obtained for both these important alternative refrigerants. The second virial coefficients for HFC-152a derived from the present sound velocity measurements agree extremely well with the reported second virial coefficient values obtained with a Burnett apparatus.Paper dedicated to Professor Joseph Kestin.  相似文献   
86.
The behavior of a premixed flame propagating from a chamber into a narrow channel at a high speed was examined using high speed and instantaneous schlieren photography, ion current measurement with electrostatic probes, and temperature measurement with an optical method. From detailed measurements of flames passing through the channel, flame extinguishment in the channel, no matter whether transient or not, was found to occur due to quenching of the reacting gas by rapid turbulent mixing with cold fresh mixture at the downstream of the contraction region and by heat transfer to the cold channel walls. Extinguishment must occur when these heat losses exceed the heat released by the chemical reaction of the flowing mixture.  相似文献   
87.
The anti-tumor and anti-metastatic effects of O-(chloroacetyl-carbamoyl) fumagillol (TNP-470), an angiogenesis inhibitor, and cisplatin (CDDP), an anti-neoplastic agent, were investigated using our established liver-metastasizing pancreatic carcinoma line, HPC-3H4. HPC-3H4 was injected into the spleens of nude mice. Mice were randomly divided into 5 groups; a control group given saline solution, a group receiving 45 mg/kg TNP-470, a group receiving 90 mg/kg TNP-470, a group receiving 90 mg/kg TNP-470 in combination with 0.25 mg/kg CDDP, and a group receiving 0.25 mg/kg CDDP. In the control group, liver metastasis developed in 14 of 15 mice (93.3%). Liver metastasis developed in 9 of 11 mice (81.8%) receiving 0.25 mg/kg CDDP. It developed in 11 of 15 mice (73.3%) receiving 45 mg/kg TNP-470, in 17 of 18 mice (94.4%) receiving 90 mg/kg TNP-470, and in 4 of 10 mice (40%) receiving 90 mg/kg TNP-470 in combination with 0.25 mg/kg CDDP. TNP-470 in combination with CDDP displayed a significant inhibitory effect on liver metastasis compared to the control. Although TNP-470 alone and CDDP alone had no effect on the tumor growth in vivo, 90 mg/kg TNP-470 in combination with 0.25 mg/kg CDDP had a significant effect. In vitro examinations demonstrated that the growth of HPC-3H4 cells was only mildly inhibited by TNP-470, but the production of vascular endothelial growth factor (VEGF) by HPC-3H4 was clearly inhibited by TNP-470. The inhibitory effect on the production of VEGF was not strong with CDDP treatment. These results indicate that the angiogenesis inhibitor TNP-470 in combination with low-dose CDDP has inhibitory activity against liver metastasis of human pancreatic carcinoma.  相似文献   
88.
BACKGROUND: In an effort to intensify osteosarcoma therapy, systemic ifosfamide was added pre- and postoperatively to an already aggressive three-drug regimen. In a subgroup of patients, loco-regional treatment intensification was attempted by using the intraarterial route to give cisplatin. PATIENTS AND METHODS: Patients < or = 40 years at diagnosis of a localised, de novo high-grade central extremity osteosarcoma were eligible for inclusion into study COSS-86 if registered within three weeks from biopsy. Doxorubicin, high-dose methotrexate, and cisplatin were given to all patients. Patients who fulfilled one or more of three defined high-risk criteria received early systemic treatment intensification by adding ifosfamide as the fourth agent. Preoperatively, these high-risk patients received cisplatin either intraarterially or intravenously. RESULTS: 171 eligible patients were entered, of which 128 were stratified into the high-risk group. When all 171 were analysed by intention-to-treat, actuarial overall and event-free survival rates at ten years were 72% and 66%, respectively. No benefit of intraarterial cisplatin application was detected. Cumulative treatment toxicity was considerable. CONCLUSIONS: In a multicenter setting, intensive treatment of osteosarcoma according to protocol COSS-86 led to long-term disease-free survival for two thirds of patients. We saw no benefit of using the intraarterial route to administer cisplatin.  相似文献   
89.
Ligand binding to neurotransmitter and hormone receptors which couple to the Gq subclass of GTP-binding protein leads to the activation of phospholipase Cbeta (PLCbeta) which hydrolyses phosphatidyl-inositol 4,5-bisphosphate, yielding a pair of second messengers, diacylglycerol and inositol 1,4,5-trisphosphate (IP3). The expression of PLCbeta1-4 mRNAs was comparatively examined by in situ hybridization in the mouse brain. In adults, PLCbeta1 mRNA was expressed predominantly in the telencephalon, including the cerebral cortex, hippocampus, amygdala, lateral septum and olfactory bulb, with little expression in most thalamic nuclei. PLCbeta2 mRNA was distributed in the white matter, suggesting its expression in non-neuronal cells, most likely oligodendrocytes. PLCbeta3 mRNA was specifically expressed in cerebellar Purkinje cells. The highest levels of PLCbeta4 mRNA were detected in Purkinje cells. High levels of PLCbeta4 mRNA were also found in the thalamus and medial septum, whereas weak signals were detected in most telencephalic regions, thus showing an expression pattern almost reciprocal to that of PLCbeta1 mRNA. During development, such characteristic regional expression of PLCbeta1 and PLCbeta4 were observed starting in late foetal stages, while specific expression of PLCbeta2 and PLCbeta3 appeared in early postnatal stages. We conclude that despite the existence of four PLCbeta isoforms, only one or two of them is expressed in individual neurons and glial cells. The distinct expression of PLCbetas provides a molecular basis for analysing the nature of the specific signal transduction pathway leading to the production of diacylglycerol and IP3 in distinct cell types and in different regions of the brain.  相似文献   
90.
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