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   84339篇
  免费   7449篇
  国内免费   4534篇
电工技术   5014篇
技术理论   3篇
综合类   8208篇
化学工业   13144篇
金属工艺   4479篇
机械仪表   5235篇
建筑科学   6007篇
矿业工程   2042篇
能源动力   2192篇
轻工业   7732篇
水利工程   1759篇
石油天然气   3363篇
武器工业   672篇
无线电   9802篇
一般工业技术   9054篇
冶金工业   3606篇
原子能技术   1212篇
自动化技术   12798篇
  2024年   107篇
  2023年   942篇
  2022年   1624篇
  2021年   2445篇
  2020年   1990篇
  2019年   1671篇
  2018年   1788篇
  2017年   2072篇
  2016年   1923篇
  2015年   2869篇
  2014年   3973篇
  2013年   4923篇
  2012年   5849篇
  2011年   6341篇
  2010年   5972篇
  2009年   5851篇
  2008年   5874篇
  2007年   5631篇
  2006年   5486篇
  2005年   4585篇
  2004年   3748篇
  2003年   3334篇
  2002年   3918篇
  2001年   3377篇
  2000年   2330篇
  1999年   1699篇
  1998年   1089篇
  1997年   918篇
  1996年   836篇
  1995年   725篇
  1994年   549篇
  1993年   396篇
  1992年   323篇
  1991年   242篇
  1990年   205篇
  1989年   132篇
  1988年   123篇
  1987年   85篇
  1986年   43篇
  1985年   62篇
  1984年   44篇
  1983年   31篇
  1982年   22篇
  1981年   25篇
  1980年   16篇
  1979年   20篇
  1978年   11篇
  1977年   16篇
  1976年   22篇
  1951年   9篇
排序方式: 共有10000条查询结果,搜索用时 70 毫秒
1.
Heparanase (Hpse) is an endo-β-D-glucuronidase capable of cleaving heparan sulfate side chains. Its upregulated expression is implicated in tumor growth, metastasis and angiogenesis, thus making it an attractive target in cancer therapeutics. Currently, a few small molecule inhibitors have been reported to inhibit Hpse, with promising oral administration and pharmacokinetic (PK) properties. In the present study, a ligand-based pharmacophore model was generated from a dataset of well-known active small molecule Hpse inhibitors which were observed to display favorable PK properties. The compounds from the InterBioScreen database of natural (69,034) and synthetic (195,469) molecules were first filtered for their drug-likeness and the pharmacophore model was used to screen the drug-like database. The compounds acquired from screening were subjected to molecular docking with Heparanase, where two molecules used in pharmacophore generation were used as reference. From the docking analysis, 33 compounds displayed higher docking scores than the reference and favorable interactions with the catalytic residues. Complex interactions were further evaluated by molecular dynamics simulations to assess their stability over a period of 50 ns. Furthermore, the binding free energies of the 33 compounds revealed 2 natural and 2 synthetic compounds, with better binding affinities than reference molecules, and were, therefore, deemed as hits. The hit compounds presented from this in silico investigation could act as potent Heparanase inhibitors and further serve as lead scaffolds to develop compounds targeting Heparanase upregulation in cancer.  相似文献   
2.
Catalysis Letters - We converted agro-waste Custard Apple Peels (CAP) to ash via thermal treatment, on which Pd(OAc)2 was immobilized easily that produced a low-cost, highly efficient Pd/CAP-ash...  相似文献   
3.
Background: Recently, it was reported that leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4, also called GPR48) is another receptor for RANKL and was shown to compete with RANK to bind RANKL and suppress canonical RANK signaling during osteoclast differentiation. The critical role of the protein triad RANK–RANKL in osteoclastogenesis has made their binding an important target for the development of drugs against osteoporosis. In this study, point-mutations were introduced in the RANKL protein based on the crystal structure of the RANKL complex and its counterpart receptor RANK, and we investigated whether LGR4 signaling in the absence of the RANK signal could lead to the inhibition of osteoclastogenesis.; Methods: The effects of point-mutated RANKL (mRANKL-MT) on osteoclastogenesis were assessed by tartrate-resistant acid phosphatase (TRAP), resorption pit formation, quantitative real-time polymerase chain reaction (qPCR), western blot, NFATc1 nuclear translocation, micro-CT and histomorphological assay in wild type RANKL (mRANKL-WT)-induced in vitro and in vivo experimental mice model. Results: As a proof of concept, treatment with the mutant RANKL led to the stimulation of GSK-3β phosphorylation, as well as the inhibition of NFATc1 translocation, mRNA expression of TRAP and OSCAR, TRAP activity, and bone resorption, in RANKL-induced mouse models; and Conclusions: The results of our study demonstrate that the mutant RANKL can be used as a therapeutic agent for osteoporosis by inhibiting RANKL-induced osteoclastogenesis via comparative inhibition of RANKL. Moreover, the mutant RANKL was found to lack the toxic side effects of most osteoporosis treatments.  相似文献   
4.
The Ag-Pd internal electrode of multilayer piezoelectric ceramics needs to be sintered below 1000°C, and lead wires and components need to be welded with lead-free solder at 260°C. PNN–PMW–PZT–xSr piezoelectric ceramics with high Curie temperature (Tc > 260°C) were synthesized at a low sintering temperature (960°C) to meet the requirements of multilayer piezoelectric devices. The relationship between structures (phase, domain, and microstructures) and electrical properties (piezo/ferroelectric properties, and dielectric relaxation) in the Sr2+ substituted ceramics was investigated. Rietveld refinement and Raman spectra show that Sr2+ substitution can cause the phase change and increase the force constant of [BO6] octahedron. The piezoelectric response increases with increasing the content of the tetragonal phase (CTP) in the rhombohedral-tetragonal (R-T) coexisted ceramics. The ceramics with 0.6 mol% Sr2+ substitution have minimum activation energy for domain wall movement (Ea) of 0.0362 eV which favors the formation of nanometer-sized domains, and possess excellent electrical properties (d33 = 623 pC/N, d33* =783 pm/V, Tc =295°C). The higher the CTP, the lower the Ea. The lower Ea favors the rotation of polarization direction and extension, and is beneficial to the generation of the nanometer-size domains, resulting in high piezoelectric properties.  相似文献   
5.
洪礼武 《大氮肥》2021,44(2):124-126
在传统检测手段无法满足越来越趋向大型化、超大型化的塔器整体两侧直线度的过程检测和控制保障背景下,打破传统思维,大胆创新检测手段,自行设计开发出超大型塔器整体两侧直线度检测整套技术,充分解决超大型塔器整体两侧直线度的检测难题.  相似文献   
6.
平台支持船由于作业需要通常配备有动力定位系统,其在侧推工况下舱室噪声超标较为严重。针对这个问题采用计算流体力学(CFD)方法,得到侧推螺旋桨作用在导管上的脉动压力,并将时域计算结果转换成噪声计算的激励条件。采用有限元(FE)与统计能量分析(SEA)混合方法建立船体中频段FE-SEA耦合模型并建立船体高频段SEA模型,对某65 m AHTS船侧推工况下全频段(63 Hz~8000 Hz)舱室噪声进行预报,分析该船噪声分布规律及主要影响因素。并建立起全船的SEA模型,在中频段对比SEA与FE-SEA两种方法得到的舱室声压级频谱曲线,验证了使用混合模型的必要性。  相似文献   
7.
位于巴音戈壁盆地南部的塔木素铀矿床在矿化特征上明显有别于我国北方其他砂岩型铀矿床,对于该矿床的成因也存在较大的争议。通过岩石学、同位素地质学、扫描电子显微镜、阴极发光、径迹蚀刻等综合研究,结果显示塔木素铀矿床巴音戈壁组上段第三岩性段(K 1 b 2-3)含铀泥灰岩至少经历了4个阶段的成岩作用,铀矿物呈微粒(粒径<1μm)浸染状分布于最早期的角砾中,具有沉积成岩成因特征,成矿物质主要来自于沉积成岩期水体中溶解的铀并因蒸发浓缩作用而富集在特定的层位。巴音戈壁组上段第二岩性段(K 1 b 2-2)含铀砂岩在沉积成岩阶段盆地内封存的高矿化度地下水与碎屑物之间以及成岩后酸性地表水与碳酸盐胶结物之间共发生了两个阶段的水岩作用,每个阶段形成了表现特征不同的铀矿化。沥青铀矿U-Pb同位素测试结果显示,区内最早的铀矿化形成时间为111.6±8.1 Ma,与砂岩形成时间接近,而最新的铀矿化形成时间为2.5 Ma,具有明显后生成因特征,综合研究显示砂岩中的铀矿化具有沉积成岩及后期层间氧化叠加改造双重成因特征,沉积成岩期成矿物质主要来自封存的地下水,而层间氧化期成矿物质主要来自地表水带入的铀及富铀岩层。同时研究认为塔木素铀矿床存在后期热液活动,但暂未发现热液活动与铀成矿具有直接的成因联系。  相似文献   
8.
While the challenges associated with the stability of metal halide perovskites are well known and intensely studied, variability in electronic properties represents an equally significant, yet seldom studied, challenge that could potentially slow or inhibit the commercial viability of these systems. In this work, the contactless characterization technique time-resolved microwave conductivity (TRMC) is used to quantify the variability in electronic properties of the prototypical perovskite, methylammonium lead iodide (MAPbI3) both between different samples, and at different locations within the same sample. Using scanning electron microscopy (SEM) and a quasi-automated image-analysis strategy, it is possible to evaluate the metrics of heterogeneity in surface microstructure and correlate them with the electronic properties as obtained by TRMC. Substantial intra-sample and inter-sample variation is observed in the mobility-yield product in samples prepared following differing protocols, and in samples prepared following identical protocols.  相似文献   
9.
建立了一种快速、灵敏测定药物中盐酸美西律的双波长分光光度法。在弱碱性溶液中,虎红与盐酸美西律反应生成离子缔合物,使溶液发生褪色现象,光谱曲线上呈现2个较强的负吸收峰,它们分别位于472和560 nm,在此2个波长处,盐酸美西律的线性范围为0.04~2.6 mg/L,表观摩尔吸光系数(κ)分别为5.87×104(472 nm)和3.59×104 L/(mol·cm)(560 nm),检出限为0.033(472 nm)和0.035 mg/L(560 nm)。用双波长法测定时,其表观摩尔吸光系数(κ)达9.46×104 L/(mol·cm),检出限为0.017 mg/L。双波长法用于盐酸美西律药片测定,加标回收率为97.7%~103%,相对标准偏差(RSD)为2.2%~2.6%。  相似文献   
10.
王文高  张红 《玻璃》2021,48(3):48-52
阐述了建筑用夹层玻璃产品检测中一些常见的质量问题,对其产生的原因进行分析,并对建筑用夹层玻璃的生产和质量管理提出建议.  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