全文获取类型
收费全文 | 53328篇 |
免费 | 8928篇 |
国内免费 | 5423篇 |
学科分类
工业技术 | 67679篇 |
出版年
2024年 | 590篇 |
2023年 | 1622篇 |
2022年 | 2643篇 |
2021年 | 2853篇 |
2020年 | 2808篇 |
2019年 | 2166篇 |
2018年 | 1843篇 |
2017年 | 2333篇 |
2016年 | 2451篇 |
2015年 | 2770篇 |
2014年 | 4297篇 |
2013年 | 3764篇 |
2012年 | 4464篇 |
2011年 | 4691篇 |
2010年 | 3534篇 |
2009年 | 3458篇 |
2008年 | 3505篇 |
2007年 | 3737篇 |
2006年 | 3020篇 |
2005年 | 2511篇 |
2004年 | 1880篇 |
2003年 | 1537篇 |
2002年 | 1149篇 |
2001年 | 798篇 |
2000年 | 636篇 |
1999年 | 490篇 |
1998年 | 411篇 |
1997年 | 294篇 |
1996年 | 283篇 |
1995年 | 199篇 |
1994年 | 136篇 |
1993年 | 121篇 |
1992年 | 113篇 |
1991年 | 97篇 |
1990年 | 82篇 |
1989年 | 41篇 |
1988年 | 50篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 30篇 |
1984年 | 28篇 |
1983年 | 24篇 |
1982年 | 18篇 |
1981年 | 26篇 |
1980年 | 25篇 |
1979年 | 9篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1966年 | 8篇 |
1963年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
132.
Antibiotic and multi-drug resistant (MDR) Salmonella poses a significant threat to public health due to its ability to colonize animals (cold and warm-blooded) and contaminate freshwater supplies. Monitoring antibiotic resistant Salmonella is traditionally costly, involving the application of phenotypic and genotypic tests over several days. However, with the introduction of cheaper semi-automated devices in the last decade, strain detection and identification times have significantly fallen. This, in turn, has led to efficiently regulated food production systems and further reductions in food safety hazards. This review highlights current and emerging technologies used in the detection of antibiotic resistant and MDR Salmonella. 相似文献
133.
The objective of this study is to identify defects such as surface cracks, subsurface defects and metal losses using feature based pulsed eddy current sensors. A new feature, termed as the rising point, related to the propagation time of electromagnetic waves in metallic targets is proposed for defect classification. Experimental studies of the validation, robustness of the new feature of rising time are reported. In addition to other features, defects can be detected and quantified robustly and lift-off can also be derived from the rising time. Conclusion and further work are derived on the basis of the findings. 相似文献
134.
魏惠元 《稀有金属材料与工程》1992,21(5):64-68
针对钛、钢焊缝X射线照相探伤中,要通过实验来确定管电压值,存在低效、浪费的问题,作者总结大量探伤工作中的数据,找出了对于不同透照方式和不同透照条件下,管电压值与试样厚度和透照距离之间的关系,建立了计算管电压值的经验公式,并对计算值与实验值作了对比分析,证实经验公式简便可靠。文中给出了适用于国内广泛采用的几种X光探伤机和通用的几种感光胶片的管电压计算公式及有关数据,可供钛、钢X光探伤工作者参考应用。 相似文献
135.
136.
137.
W. Dennis Pocklington 《Journal of the American Oil Chemists' Society》1992,69(8):789-793
The development, by collaborative study, of a standardized method for the determination of tetrachloroethylene in olive oils
is described. The results of the study, which was carried out in 1989 under the direction of the International Olive Oil Council
(IOOC), are presented and show that tetrachloroethylene can be readily determined, to an acceptable degree of precision, by
gas-liquid chromatography with electron capture detection. A limited number of results obtained for the determination of trichloroethylene
and chloroform by the same method indicate that a similar precision could be obtained with the method when determining these
solvents also. 相似文献
138.
两性离子表面活性剂在分析化学中的应用 总被引:1,自引:0,他引:1
综述了两性离子表面活性剂在分析检测尤其在色谱分离和毛细管电泳技术中的应用。在色谱分离中,两性表面活性剂首先被用作固定相,能很好地分离海水及雨水中的阴离子;后来随着色谱技术在生物领域的应用,两性表面活性剂又被用作流动相,即把其溶解于电解质溶液中,此流动相能很好地分离含蛋白质的生物样品。两性表面活性剂还被广泛地用于毛细管电泳中,即作毛细管壁上的动态或静态的涂层,此法既可控制电渗流,提高分离效果,又可避免蛋白质等一些样品粘在壁上,是一种较理想的生物分离技术。 相似文献
139.
140.
《Expert systems with applications》2014,41(11):5416-5430
Detecting SQL injection attacks (SQLIAs) is becoming increasingly important in database-driven web sites. Until now, most of the studies on SQLIA detection have focused on the structured query language (SQL) structure at the application level. Unfortunately, this approach inevitably fails to detect those attacks that use already stored procedure and data within the database system. In this paper, we propose a framework to detect SQLIAs at database level by using SVM classification and various kernel functions. The key issue of SQLIA detection framework is how to represent the internal query tree collected from database log suitable for SVM classification algorithm in order to acquire good performance in detecting SQLIAs. To solve the issue, we first propose a novel method to convert the query tree into an n-dimensional feature vector by using a multi-dimensional sequence as an intermediate representation. The reason that it is difficult to directly convert the query tree into an n-dimensional feature vector is the complexity and variability of the query tree structure. Second, we propose a method to extract the syntactic features, as well as the semantic features when generating feature vector. Third, we propose a method to transform string feature values into numeric feature values, combining multiple statistical models. The combined model maps one string value to one numeric value by containing the multiple characteristic of each string value. In order to demonstrate the feasibility of our proposals in practical environments, we implement the SQLIA detection system based on PostgreSQL, a popular open source database system, and we perform experiments. The experimental results using the internal query trees of PostgreSQL validate that our proposal is effective in detecting SQLIAs, with at least 99.6% of the probability that the probability for malicious queries to be correctly predicted as SQLIA is greater than the probability for normal queries to be incorrectly predicted as SQLIA. Finally, we perform additional experiments to compare our proposal with syntax-focused feature extraction and single statistical model based on feature transformation. The experimental results show that our proposal significantly increases the probability of correctly detecting SQLIAs for various SQL statements, when compared to the previous methods. 相似文献