全文获取类型
收费全文 | 502397篇 |
免费 | 54029篇 |
国内免费 | 41028篇 |
专业分类
电工技术 | 41936篇 |
技术理论 | 61篇 |
综合类 | 57504篇 |
化学工业 | 67394篇 |
金属工艺 | 18989篇 |
机械仪表 | 31225篇 |
建筑科学 | 51072篇 |
矿业工程 | 19020篇 |
能源动力 | 15316篇 |
轻工业 | 28410篇 |
水利工程 | 18541篇 |
石油天然气 | 16682篇 |
武器工业 | 5499篇 |
无线电 | 49879篇 |
一般工业技术 | 43247篇 |
冶金工业 | 20783篇 |
原子能技术 | 5879篇 |
自动化技术 | 106017篇 |
出版年
2024年 | 916篇 |
2023年 | 5971篇 |
2022年 | 10748篇 |
2021年 | 13819篇 |
2020年 | 14220篇 |
2019年 | 12234篇 |
2018年 | 11567篇 |
2017年 | 15005篇 |
2016年 | 17274篇 |
2015年 | 19633篇 |
2014年 | 27713篇 |
2013年 | 29456篇 |
2012年 | 36437篇 |
2011年 | 39464篇 |
2010年 | 30464篇 |
2009年 | 31025篇 |
2008年 | 31149篇 |
2007年 | 37821篇 |
2006年 | 35577篇 |
2005年 | 30628篇 |
2004年 | 25954篇 |
2003年 | 21920篇 |
2002年 | 17588篇 |
2001年 | 14250篇 |
2000年 | 11613篇 |
1999年 | 9367篇 |
1998年 | 7220篇 |
1997年 | 6144篇 |
1996年 | 5566篇 |
1995年 | 4824篇 |
1994年 | 4235篇 |
1993年 | 3148篇 |
1992年 | 2713篇 |
1991年 | 2091篇 |
1990年 | 1803篇 |
1989年 | 1517篇 |
1988年 | 1185篇 |
1987年 | 780篇 |
1986年 | 595篇 |
1985年 | 610篇 |
1984年 | 571篇 |
1983年 | 411篇 |
1982年 | 451篇 |
1981年 | 283篇 |
1980年 | 255篇 |
1979年 | 177篇 |
1978年 | 94篇 |
1977年 | 114篇 |
1976年 | 73篇 |
1959年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Alex Buchberger Harpinder Saini Kiarash Rahmani Eliato Azadeh Zare Ryan Merkley Yang Xu Julio Bernal Robert Ros Mehdi Nikkhah Dr. Nicholas Stephanopoulos 《Chembiochem : a European journal of chemical biology》2021,22(10):1755-1760
Biomaterials with dynamically tunable properties are critical for a range of applications in regenerative medicine and basic biology. In this work, we show the reversible control of gelatin methacrylate (GelMA) hydrogel stiffness through the use of DNA crosslinkers. We replaced some of the inter-GelMA crosslinks with double-stranded DNA, allowing for their removal through toehold-mediated strand displacement. The crosslinks could be restored by adding fresh dsDNA with complementary handles to those on the hydrogel. The elastic modulus (G’) of the hydrogels could be tuned between 500 and 1000 Pa, reversibly, over two cycles without degradation of performance. By functionalizing the gels with a second DNA strand, it was possible to control the crosslink density and a model ligand in an orthogonal fashion with two different displacement strands. Our results demonstrate the potential for DNA to reversibly control both stiffness and ligand presentation in a protein-based hydrogel, and will be useful for teasing apart the spatiotemporal behavior of encapsulated cells. 相似文献
62.
Rikako Tabata SungGi Chi Junichiro Yuda Yosuke Minami 《International journal of molecular sciences》2021,22(4)
Several immune checkpoint molecules and immune targets in leukemic cells have been investigated. Recent studies have suggested the potential clinical benefits of immuno-oncology (IO) therapy against acute myeloid leukemia (AML), especially targeting CD33, CD123, and CLL-1, as well as immune checkpoint inhibitors (e.g., anti-PD (programmed cell death)-1 and anti-CTLA4 (cytotoxic T-lymphocyte-associated protein 4) antibodies) with or without conventional chemotherapy. Early-phase clinical trials of chimeric antigen receptor (CAR)-T or natural killer (NK) cells for relapsed/refractory AML showed complete remission (CR) or marked reduction of marrow blasts in a few enrolled patients. Bi-/tri-specific antibodies (e.g., bispecific T-cell engager (BiTE) and dual-affinity retargeting (DART)) exhibited 11–67% CR rates with 13–78% risk of cytokine-releasing syndrome (CRS). Conventional chemotherapy in combination with anti-PD-1/anti-CTLA4 antibody for relapsed/refractory AML showed 10–36% CR rates with 7–24 month-long median survival. The current advantages of IO therapy in the field of AML are summarized herein. However, although cancer vaccination should be included in the concept of IO therapy, it is not mentioned in this review because of the paucity of relevant evidence. 相似文献
63.
为了实现在工业化生产中对α钛富氧层厚度预测和控制,通过实验研究α钛富氧层在高温空气环境中的形成及增厚过程,讨论热处理温度和时间的影响作用,建立高温(750~850℃)空气环境下关于温度、时间的富氧层增厚动力学模型。结果表明:当恒温热处理温度为750~850℃时,α钛富氧层厚度x与保温时间t0.5呈正比例关系,且升高热处理温度可显著提高富氧层增厚速度。在此温度范围内,氧原子的扩散激活能约为203473 J/mol,计算曲线与实验数据吻合性较好。结合文献中已有的扩散系数方程和实验测得的富氧层厚度数据,推导得到5个富氧层增厚动力学方程,其中3个方程的计算曲线与实验数据吻合性较好,可为实际生产中预估富氧层厚度提供理论支持。 相似文献
64.
Felipe A. Perdomo Siti H. Khalit Claire S. Adjiman Amparo Galindo George Jackson 《American Institute of Chemical Engineers》2021,67(3):e17194
The SAFT-γ Mie group-contribution equation of state is used to represent the fluid-phase behavior of aqueous solutions of a variety of linear, branched, and cyclic amines. New group interactions are developed in order to model the mixtures of interest, including the like and unlike interactions between alkyl primary, secondary, and tertiary amine groups (NH2, NH, N), cyclic secondary and tertiary amine groups (cNH, cN), and cyclic methine-amine groups (cCHNH, cCHN) with water (H2O). The group-interaction parameters are estimated from appropriate experimental thermodynamic data for pure amines and selected mixtures. By taking advantage of the group-contribution nature of the method, one can describe the fluid-phase behavior of mixtures of molecules comprising those groups over broad ranges of temperature, pressure, and composition. A number of aqueous solutions of amines are studied including linear, branched aliphatic, and cyclic amines. Liquid–liquid equilibria (LLE) bounded by lower critical solution temperatures (LCSTs) have been reported experimentally and are reproduced here with the SAFT-γ Mie approach. The main feature of the approach is the ability not only to represent accurately the experimental data employed in the parameter estimation, but also to predict the vapor–liquid, liquid–liquid, and vapor–liquid–liquid equilibria, and LCSTs with the same set of parameters. Pure compound and binary phase diagrams of diverse types of amines and their aqueous solutions are assessed in order to demonstrate the main features of the thermodynamic and fluid-phase behavior. 相似文献
65.
66.
The effect of the emergency perception of bystanders of cyberbullying victims on helping behaviors is often neglected in research on cyberbullying. In this study, we explored the influence of this cognitive factor on cyber-bystanders’ helping tendencies as well as elucidated possible underlying processes. The results of two studies were reported. In Study 1, 150 undergraduates read a true case of a girl experiencing cyberbullying. The results indicated that when the participants perceived the victim’s situation to be more critical (i.e., higher emergency perception), their helping tendencies were stronger, partly through increased state empathy followed by feelings of responsibility to help. In Study 2, we randomly assigned 300 undergraduates to two groups. The low emergency group read the same cyberbullying case as Study 1, whereas the cyberbullying case read by the high emergency group contained additional emergency information of the victim. The results indicated that the high emergency group expressed stronger helping tendencies than did the low emergency group. This effect was caused by a stronger perception that the victim was in an emergency situation, which not only strengthened the participants’ helping tendencies directly but also indirectly through increasing their state empathy and feelings of responsibility to help. 相似文献
67.
目的 赣傩艺术元素内容丰富并保存完整,是研究我国古代赣傩地区文化与艺术的珍贵史料.研究赣傩艺术元素的提取及衍生图案的设计方法,在设计应用中表达赣傩傩面具、选取傩舞形和构筑傩庙魂,能给当代赣傩艺术元素的产品设计以指引.方法 通过直接引用、形意结合和局部强化的设计方法,增厚其丰富内涵、设计个性和主题意蕴.通过现代化审美中"绿色化、感性化、地域化"的要求,遵循"以退为进,化繁为简""多元并存,个性体现"的原则,强化赣傩艺术元素的独特风格.结论 用现代的手法,将特色的赣傩艺术元素植入到理性的产品设计中去,使赣傩艺术元素与现代设计思想有机结合.在继承传统文化与现代流行中找到契合点,深入挖掘赣傩艺术元素蕴含的文化精神、文化胸怀和文化自信,使中华传统文化在现代审美下进行创新再现. 相似文献
68.
梯度分层铝合金蜂窝板是一种有效的吸能结构,本工作在梯度铝蜂窝结构的基础上根据梯度率的概念,通过改变蜂窝芯层的胞壁长度,设计了4种质量相同、梯度率不同的铝蜂窝夹芯结构。通过准静态压缩实验,并结合非线性有限元模拟准静态及冲击态下梯度铝蜂窝夹芯结构的变形情况及其力学性能,分析对比了相同质量下梯度铝蜂窝夹芯结构在准静态下的变形模式以及冲击载荷下分层均质蜂窝结构和不同梯度率的分层梯度蜂窝结构的动态响应和能量吸收特性。结果表明:在准静态压缩过程中,铝蜂窝梯度夹芯板的变形具有明显的局部化特征,蜂窝芯的变形为低密度优先变形直至密实,层级之间的密实化应变差随芯层密度的增大而逐渐减小;在高速冲击下,梯度蜂窝板并非严格按照准静态过程中逐级变形直至密实,而是在锤头冲击惯性及芯层密度的相互作用下整体发生的线弹性变形、弹性屈曲、塑性坍塌及密实化;另外,在本工作所设计的梯度率中,当梯度率为γ1=0.0276时,梯度蜂窝夹芯板的吸能性达到最好,相较于同等质量下的均质蜂窝夹芯板,能量吸收提高了10.63%。 相似文献
69.
为了建立一种准确性高、成本低的植物油中苯并(a)芘测定的样品前处理方法,基于GB 5009.7—2016以自制氧化铝柱为固相萃取柱,采用单因素试验对称样量、洗脱剂量、洗脱流速、吸附剂存放时间、吸附剂量这5个影响植物油中苯并(a)芘洗脱的因素进行研究,优化前处理条件,并对测定方法进行考察。结果表明:优化的前处理条件为称样量0.100 0 g、洗脱剂量120 mL、吸附剂(氧化铝)量22 g、洗脱流速1滴/2 s、吸附剂存放时间少于12周;方法检出限为0.2 μg/L,样品加标回收率为94.23%~100.00%,RSD为1.20%~7.36%;同一样品测定结果与SGS测定值接近,相对平均偏差为2.36%~3.50%。说明本试验方法测定结果准确,可应用于油脂企业植物油中痕量苯并(a)芘的测定。 相似文献
70.
Cheng-Chin Huang Ching-Yao Yang Chin-Chuan Su Kai-Min Fang Cheng-Chieh Yen Ching-Ting Lin Jui-Min Liu Kuan-I Lee Ya-Wen Chen Shing-Hwa Liu Chun-Fa Huang 《International journal of molecular sciences》2021,22(9)
4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), a major active metabolite of bisphenol A (BPA), is generated in the mammalian liver. Some studies have suggested that MBP exerts greater toxicity than BPA. However, the mechanism underlying MBP-induced pancreatic β-cell cytotoxicity remains largely unclear. This study demonstrated the cytotoxicity of MBP in pancreatic β-cells and elucidated the cellular mechanism involved in MBP-induced β-cell death. Our results showed that MBP exposure significantly reduced cell viability, caused insulin secretion dysfunction, and induced apoptotic events including increased caspase-3 activity and the expression of active forms of caspase-3/-7/-9 and PARP protein. In addition, MBP triggered endoplasmic reticulum (ER) stress, as indicated by the upregulation of GRP 78, CHOP, and cleaved caspase-12 proteins. Pretreatment with 4-phenylbutyric acid (4-PBA; a pharmacological inhibitor of ER stress) markedly reversed MBP-induced ER stress and apoptosis-related signals. Furthermore, exposure to MBP significantly induced the protein phosphorylation of JNK and AMP-activated protein kinase (AMPK)α. Pretreatment of β-cells with pharmacological inhibitors for JNK (SP600125) and AMPK (compound C), respectively, effectively abrogated the MBP-induced apoptosis-related signals. Both JNK and AMPK inhibitors also suppressed the MBP-induced activation of JNK and AMPKα and of each other. In conclusion, these findings suggest that MBP exposure exerts cytotoxicity on β-cells via the interdependent activation of JNK and AMPKα, which regulates the downstream apoptotic signaling pathway. 相似文献