全文获取类型
收费全文 | 33088篇 |
免费 | 871篇 |
国内免费 | 64篇 |
专业分类
电工技术 | 368篇 |
综合类 | 35篇 |
化学工业 | 6790篇 |
金属工艺 | 858篇 |
机械仪表 | 623篇 |
建筑科学 | 1841篇 |
矿业工程 | 247篇 |
能源动力 | 1016篇 |
轻工业 | 2762篇 |
水利工程 | 337篇 |
石油天然气 | 207篇 |
武器工业 | 2篇 |
无线电 | 2150篇 |
一般工业技术 | 5204篇 |
冶金工业 | 6642篇 |
原子能技术 | 323篇 |
自动化技术 | 4618篇 |
出版年
2022年 | 196篇 |
2021年 | 386篇 |
2020年 | 335篇 |
2019年 | 399篇 |
2018年 | 488篇 |
2017年 | 509篇 |
2016年 | 522篇 |
2015年 | 463篇 |
2014年 | 736篇 |
2013年 | 2132篇 |
2012年 | 1241篇 |
2011年 | 1590篇 |
2010年 | 1169篇 |
2009年 | 1258篇 |
2008年 | 1436篇 |
2007年 | 1466篇 |
2006年 | 1256篇 |
2005年 | 1172篇 |
2004年 | 1052篇 |
2003年 | 1023篇 |
2002年 | 1031篇 |
2001年 | 634篇 |
2000年 | 615篇 |
1999年 | 575篇 |
1998年 | 600篇 |
1997年 | 499篇 |
1996年 | 604篇 |
1995年 | 546篇 |
1994年 | 532篇 |
1993年 | 534篇 |
1992年 | 486篇 |
1991年 | 321篇 |
1990年 | 438篇 |
1989年 | 424篇 |
1988年 | 379篇 |
1987年 | 425篇 |
1986年 | 382篇 |
1985年 | 515篇 |
1984年 | 491篇 |
1983年 | 443篇 |
1982年 | 464篇 |
1981年 | 445篇 |
1980年 | 353篇 |
1979年 | 365篇 |
1978年 | 329篇 |
1977年 | 307篇 |
1976年 | 268篇 |
1975年 | 318篇 |
1974年 | 243篇 |
1973年 | 279篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
John R. Hamburg Roger L. Creighton 《Journal of the American Planning Association. American Planning Association》2013,79(2):67-72
The planning of community facilities requires accurate quantitative estimates of the area, type, intensity, and location of land uses required by the growth of urban activities. The distribution of these activities and the intensity of their use of land are highly related to accessibility as measured by distance from the CBD. This paper outlines a procedure whereby area-wide estimates of future population and economic activity can be distributed to small subareas so that measures of local land requirements may be obtained. 相似文献
22.
23.
John Egan 《Natural Gas \u0026amp; Electricity》2017,34(2):21-26
In Malcolm Gladwell's first book, The Tipping Point, he asked, and answered, a number of provocative questions about change, including why word-of-mouth communications continues to be so powerful. 相似文献
24.
This is the first part of a two‐part article summarizing the results of a study about why and how some businesses use “planned early dispute resolution” systems. 相似文献
25.
Comparative Cytotoxicity of Artemisinin and Cisplatin and Their Interactions with Chlorogenic Acids in MCF7 Breast Cancer Cells 下载免费PDF全文
Dr. John O. Suberu Dr. Isolda Romero‐Canelón Dr. Neil Sullivan Prof. Alexei A. Lapkin Dr. Guy C. Barker 《ChemMedChem》2014,9(12):2791-2797
In parts of Africa and Asia, self‐medication with a hot water infusion of Artemisia annua (Artemisia tea) is a common practice for a number of ailments including malaria and cancer. In our earlier work, such an extract showed better potency than artemisinin alone against both chloroquine‐sensitive and ‐resistant parasites. In this study, in vitro tests of the infusion in MCF7 cells showed high IC50 values (>200 μM ). The combination of artemisinin and 3‐caffeoylquinic acid (3CA), two major components in the extract, was strongly antagonistic and gave a near total loss of cytotoxicity for artemisinin. We observed that the interaction of 3CAs with another cytotoxic compound, cisplatin, showed potentiation of activity by 2.5‐fold. The chelation of cellular iron by 3CA is hypothesized as a possible explanation for the loss of artemisinin activity. 相似文献
26.
27.
28.
Wenya Wang Xi Zheng Anca Azoitei Axel John Friedemann Zengerling Felix Wezel Christian Bolenz Cagatay Günes 《International journal of molecular sciences》2022,23(22)
TKS5 promotes invasion and migration through the formation of invadopodia in some tumour cells, and it also has an important physiological function in cell migration through podosome formation in various nontumour cells. To date, the role of TKS5 in urothelial cells, and its potential role in BC initiation and progression, has not yet been addressed. Moreover, the contribution of TKS5 to ploidy control and chromosome stability has not been reported in previous studies. Therefore, in the present study, we wished to address the following questions: (i) Is TKS5 involved in the ploidy control of urothelial cells? (ii) What is the mechanism that leads to aneuploidy in response to TKS5 knockdown? (iii) Is TKS5 an oncogene or tumour-suppressor gene in the context of BC? (iv) Does TKS5 affect the proliferation, migration and invasion of BC cells? We assessed the gene and protein expressions via qPCR and Western blot analyses in a set of nontumour cell strains (Y235T, HBLAK and UROtsa) and a set of BC cell lines (RT4, T24, UMUC3 and J82). Following the shRNA knockdown in the TKS5-proficient cells and the ectopic TKS5 expression in the cell lines with low/absent TKS5 expression, we performed functional experiments, such as metaphase, invadopodia and gelatine degradation assays. Moreover, we determined the invasion and migration abilities of these genetically modified cells by using the Boyden chamber and wound-healing assays. The TKS5 expression was lower in the bladder cancer cell lines with higher invasive capacities (T24, UMUC3 and J82) compared to the nontumour cell lines from human ureter (Y235T, HBLAK and UROtsa) and the noninvasive BC cell line RT4. The reduced TKS5 expression in the Y235T cells resulted in augmented aneuploidy and impaired cell division. According to the Boyden chamber and wound-healing assays, TKS5 promotes the invasion and migration of bladder cancer cells. According to the present study, TKS5 regulates the migration and invasion processes of bladder cancer (BC) cell lines and plays an important role in genome stability. 相似文献
29.
Daniel Alexander Bizjak Lucas John Lynn Matits Alisa Uhl Sebastian Victor Waldemar Schulz Jana Schellenberg Johannes Peifer Wilhelm Bloch Manfred Weiß Beate Grüner Hendrik Bracht Jürgen Michael Steinacker Marijke Grau 《International journal of molecular sciences》2022,23(23)
Hematological and hemorheological parameters are known to be altered in COVID-19; however, the value of combined monitoring in order to deduce disease severity is only scarcely examined. A total of 44 acute SARS-CoV-2-infected patients (aCOV) and 44 age-matched healthy controls (Con) were included. Blood of aCOV was sampled at admission (T0), and at day 2 (T2), day 5 (T5), day 10 (T10), and day 30 (T30) while blood of Con was only sampled once. Inter- and intra-group differences were calculated for hematological and hemorheological parameters. Except for mean cellular volume and mean cellular hemoglobin, all blood cell parameters were significantly different between aCOV and Con. During the acute disease state (T0–T5), hematological and hemorheological parameters were highly altered in aCOV; in particular, anemic conditions and increased immune cell response/inflammation, oxidative/nitrosative stress, decreased deformability, as well as increased aggregation, were observed. During treatment and convalescence until T30, almost all abnormal values of aCOV improved towards Con values. During the acute state of the COVID-19 disease, the hematological, as well as the hemorheological system, show fast and potentially pathological changes that might contribute to the progression of the disease, but changes appear to be largely reversible after four weeks. Measuring RBC deformability and aggregation, as well as oxidative stress induction, may be helpful in monitoring critically ill COVID-19 patients. 相似文献
30.
John Amalraj Claudia E. Vergara Matías Monroy-Crdenas Ramiro Araya-Maturana Maximiliano Martínez-Cifuentes 《International journal of molecular sciences》2022,23(23)
The electrochemical behavior of N-methyl- and N-benzyl-4-piperidone curcumin analogs were studied experimentally and theoretically. The studied compounds present different substituents at the para position in the phenyl rings (-H, -Br, -Cl, -CF3, and -OCH3). We assessed their electrochemical behavior by differential pulse and cyclic voltammetry, while we employed density functional theory (DFT) M06 and M06-2x functionals along with 6-311+G(d,p) basis set calculations to study them theoretically. The results showed that compounds suffer a two-electron irreversible oxidation in the range of 0.72 to 0.86 V, with surface concentrations ranging from 1.72 × 10−7 to 5.01 × 10−7 mol/cm2. The results also suggested that the process is diffusion-controlled for all compounds. M06 DFT calculations showed a better performance than M06-2x to obtain oxidation potentials. We found a good correlation between the experimental and theoretical oxidation potential for N-benzyl-4-piperidones (R2 = 0.9846), while the correlation was poor for N-methyl-4-piperidones (R2 = 0.3786), suggesting that the latter suffer a more complex oxidation process. Calculations of the BDEs for labile C-H bonds in the compounds suggested that neither of the two series of compounds has a different tendency for a proton-coupled electron transfer (PCET) oxidation process. It is proposed that irreversible behavior is due to possible dimerization of the compounds by Shono-type oxidation. 相似文献