全文获取类型
收费全文 | 302493篇 |
免费 | 8402篇 |
国内免费 | 3966篇 |
学科分类
工业技术 | 314861篇 |
出版年
2022年 | 1973篇 |
2021年 | 3842篇 |
2020年 | 2884篇 |
2019年 | 3002篇 |
2018年 | 4117篇 |
2017年 | 4253篇 |
2016年 | 4278篇 |
2015年 | 4228篇 |
2014年 | 6315篇 |
2013年 | 14354篇 |
2012年 | 9470篇 |
2011年 | 12132篇 |
2010年 | 10094篇 |
2009年 | 10572篇 |
2008年 | 11087篇 |
2007年 | 11104篇 |
2006年 | 10529篇 |
2005年 | 9559篇 |
2004年 | 8291篇 |
2003年 | 8092篇 |
2002年 | 7844篇 |
2001年 | 7923篇 |
2000年 | 7422篇 |
1999年 | 8152篇 |
1998年 | 17875篇 |
1997年 | 12658篇 |
1996年 | 9577篇 |
1995年 | 7523篇 |
1994年 | 6577篇 |
1993年 | 6179篇 |
1992年 | 4373篇 |
1991年 | 4234篇 |
1990年 | 3822篇 |
1989年 | 3637篇 |
1988年 | 3514篇 |
1987年 | 2901篇 |
1986年 | 2881篇 |
1985年 | 3403篇 |
1984年 | 3003篇 |
1983年 | 2680篇 |
1982年 | 2502篇 |
1981年 | 2506篇 |
1980年 | 2372篇 |
1979年 | 2194篇 |
1978年 | 2156篇 |
1977年 | 2730篇 |
1976年 | 4095篇 |
1975年 | 1831篇 |
1974年 | 1733篇 |
1973年 | 1732篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Bram H. Frohock Jessica M. Gilbertie Dr. Jennifer C. Daiker Dr. Lauren V. Schnabel Dr. Joshua G. Pierce 《Chembiochem : a European journal of chemical biology》2020,21(7):933-937
The failure of frontline antibiotics in the clinic is one of the most serious threats to human health and requires a multitude of novel therapeutics and innovative approaches to treatment so as to curtail the growing crisis. In addition to traditional resistance mechanisms resulting in the lack of efficacy of many antibiotics, most chronic and recurring infections are further made tolerant to antibiotic action by the presence of biofilms. Herein, we report an expanded set of 5-benzylidene-4-oxazolidinones that are able to inhibit the formation of Staphylococcus aureus biofilms, disperse preformed biofilms, and, in combination with common antibiotics, are able to significantly reduce the bacterial load in a robust collagen-matrix model of biofilm infection. 相似文献
92.
The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions. 相似文献
93.
94.
95.
96.
Zu Guoqing Lu Yukuan Yan Yi Zhang Xiaoming Zhao Jingwei Du Wei Ran Xu Jiang Zhengyi 《Metals and Materials International》2020,26(2):248-259
Metals and Materials International - The flow behaviour and microstructure characteristics of a ferritic stainless steel were investigated using plain strain compression test on a Gleeble 3500... 相似文献
97.
Dr. Blijke S. Kroezen Gabriele Conti Benedetta Girardi Dr. Jonathan Cramer Dr. Xiaohua Jiang Dr. Said Rabbani Jennifer Müller Maja Kokot Enrico Luisoni Prof. Daniel Ricklin Dr. Oliver Schwardt Prof. Beat Ernst 《ChemMedChem》2020,15(18):1706-1719
Siglecs are members of the immunoglobulin gene family containing sialic acid binding N-terminal domains. Among them, Siglec-8 is expressed on various cell types of the immune system such as eosinophils, mast cells and weakly on basophils. Cross-linking of Siglec-8 with monoclonal antibodies triggers apoptosis in eosinophils and inhibits degranulation of mast cells, making Siglec-8 a promising target for the treatment of eosinophil- and mast cell-associated diseases such as asthma. The tetrasaccharide 6’-sulfo-sialyl Lewisx has been identified as a specific Siglec-8 ligand in glycan array screening. Here, we describe an extended study enlightening the pharmacophores of 6’-sulfo-sialyl Lewisx and the successful development of a high-affinity mimetic. Retaining the neuraminic acid core, the introduction of a carbocyclic mimetic of the Gal moiety and a sulfonamide substituent in the 9-position gave a 20-fold improved binding affinity. Finally, the residence time, which usually is the Achilles tendon of carbohydrate/lectin interactions, could be improved. 相似文献
98.
P.Y. Raval P.R. Pansara A.R. Makadiya N.H. Vasoya S.N. Dolia K.B. Modi 《Ceramics International》2018,44(15):17667-17674
The consequences of high energy mechanical milling, microwave-assisted heating and rapid thermal cooling on magnetic ordering in polycrystalline CaCu3Ti4O12 cubic perovskite have been investigated by means of X-ray powder diffractometry (300?K), dc magnetization in field – cooled and zero – field cooled modes (H = 100?Oe and 1000?Oe, T?=?5–300?K) (M – T curves) and M – H loop characteristics (T?=?5?K and 300?K, Hmax = 70?kOe). The M – T curves of unmilled and 16?h milled samples show pure antiferromagnetic and weak ferromagnetic ordering, respectively, 1?h and 6?h milled samples demonstrate the coexistence of both the phases while microwave-assisted and quenched samples exhibit classic antiferromagnetic transition and a low temperature paramagnetic–like contribution with different weights, well supported by the M – H loop characteristics. The observed transformations in the magnetic ordering are attributed to the ball-milling induced stress which curtails hybridization of empty Ti-3d orbitals with Cu-3d and O-2p orbitals and secondary phase formation. Oxygen vacancies associated with bound magnetic polarons originate ferromagnetism in the milled samples while unpaired electrons inhabited at the empty sites are the cause of paramagnetic centers. The low-temperature Curie – tail in M – T curve for quenched and microwave assisted samples is attributed to Ti3+ cations. 相似文献
99.
100.
Lecture capture with real‐time rearrangement of visual elements: impact on student performance 下载免费PDF全文
The primary goal of this study is to create and test a lecture‐capture system that can rearrange visual elements while recording is still taking place, in such a way that student performance can be positively influenced. The system we have devised is capable of integrating and rearranging multimedia sources, including learning content, the instructor and students' images, into lecture videos that are embedded in a website for students to review after school. The present study employed a two‐group experimental design, with 153 participants (145 females and 8 males) making up an experimental group in which lecture courses were recorded using the new lecture‐capture system, and 149 participants (140 females and 9 males) forming a control group whose lectures were recorded by traditional means. All participants were in the freshman college and studying Introduction to Computer and Information Science in one of six classes, and were randomly assigned to one of the two groups. The participants' midterm examination and final examination scores were collected as indicators of their academic performance, with their mathematics entrance scores used as a pre‐test. The findings obtained from analysis of covariance (ANCOVA) suggest that appropriate rearrangement of visual elements in lecture videos can significantly impact students' learning performance. 相似文献