全文获取类型
收费全文 | 354808篇 |
免费 | 3118篇 |
国内免费 | 1291篇 |
专业分类
化学 | 160471篇 |
晶体学 | 4206篇 |
力学 | 15584篇 |
综合类 | 6篇 |
数学 | 59118篇 |
物理学 | 83560篇 |
无线电 | 36272篇 |
出版年
2021年 | 2339篇 |
2020年 | 2701篇 |
2019年 | 2997篇 |
2018年 | 15296篇 |
2017年 | 14848篇 |
2016年 | 12103篇 |
2015年 | 4119篇 |
2014年 | 5282篇 |
2013年 | 11729篇 |
2012年 | 12999篇 |
2011年 | 22235篇 |
2010年 | 14215篇 |
2009年 | 14184篇 |
2008年 | 17749篇 |
2007年 | 20327篇 |
2006年 | 10718篇 |
2005年 | 11110篇 |
2004年 | 10294篇 |
2003年 | 9931篇 |
2002年 | 8659篇 |
2001年 | 7475篇 |
2000年 | 6294篇 |
1999年 | 4769篇 |
1998年 | 4340篇 |
1997年 | 4272篇 |
1996年 | 4172篇 |
1995年 | 3457篇 |
1994年 | 3479篇 |
1993年 | 3436篇 |
1992年 | 3508篇 |
1991年 | 3593篇 |
1990年 | 3426篇 |
1989年 | 3335篇 |
1988年 | 3225篇 |
1987年 | 2931篇 |
1986年 | 2843篇 |
1985年 | 3672篇 |
1984年 | 3778篇 |
1983年 | 3037篇 |
1982年 | 3358篇 |
1981年 | 3212篇 |
1980年 | 3020篇 |
1979年 | 3169篇 |
1978年 | 3240篇 |
1977年 | 3231篇 |
1976年 | 3161篇 |
1975年 | 3027篇 |
1974年 | 3003篇 |
1973年 | 3158篇 |
1972年 | 2102篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
I A Bukaeva L A Iakovleva B A Lapin L V Indzhiia E M Kobe 《Eksperimental?nai?a onkologii?a》1987,9(4):26-30
The results of morphological study of B- and T-cellular immunoblast baboon lymphomas are presented. Differences are found both in the structure of tumour cells and in the histostructure of tumours as a whole. The tumor cells of B-immunoblastic lymphomas expressed mainly IgM. The tumour cells of certain T-immunoblastic lymphomas being investigated by means of monoclonal OKT4 antibodies had a surface phenotype peculiar to T-helper cells. 相似文献
123.
Many analyses of boxed microstrip discontinuities require the location of large numbers of high-order modes. Using Sturm-Liouville theory, this letter derives a relationship between microstrip modes and slab-loaded guide modes, leading to an efficient mode location algorithm for microstrip, including microstrip with finite strip thickness.<> 相似文献
124.
Removing noise from audio signals requires a nondiagonal processing of time-frequency coefficients to avoid producing ldquomusical noise.rdquo State of the art algorithms perform a parameterized filtering of spectrogram coefficients with empirically fixed parameters. A block thresholding estimation procedure is introduced, which adjusts all parameters adaptively to signal property by minimizing a Stein estimation of the risk. Numerical experiments demonstrate the performance and robustness of this procedure through objective and subjective evaluations. 相似文献
125.
The known plant growth regulator, Al'den [1-(3,7-dimethyloctyl)-1-allylpiperidinium bromide], and also 1-(3,7-dimethyloctyl)-1-methylpiperidinium iodide were synthesized by treatment with allyl bromide and methyl iodide, respectively, of exhaustively hydrogenated 1-nerylpiperidine which was obtained by anionic telomerization of isoprene with piperidine. Various quaternary ammonium salts having a terpene sub- stituent with unnatural dimethyloctane skeleton, which effectively stimulate florification of Aster Chinensis L., were prepared by the action of alkyl halides on telomerization products derived from isoprene and piperidine or morpholine in the presence of palladium complexes. 相似文献
126.
127.
C. Vaca‐Garcia G. Gozzelino W. G. Glasser M. E. Borredon 《Journal of Polymer Science.Polymer Physics》2003,41(3):281-288
The main transitions of cellulose fatty esters with different degrees of substitution (DSs) were investigated with dynamic mechanical thermal analysis. Two distinct main relaxations were observed in partially substituted cellulose esters (PSCEs). They were attributed to the glass‐transition temperature and to the chain local motion of the aliphatic substituents. The temperatures of both transitions decreased when DS or the number of carbon atoms (n) of the acyl substituent increased. Conversely, all the transitions of fully substituted cellulose esters occurred within a narrow temperature range, and they did not vary significantly with n. This phenomenon was explained by the formation of a crystalline phase of the fatty substituents. The presence of few residual OH groups in PSCEs was responsible for a large increase in the storage bending modulus, and it eliminated the effect of n on damping. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 281–288, 2003 相似文献
128.
129.
130.
Fix integers m, n such that 1 ≤ m ≤ n ? 3. Let X ? Pn be an integral non-degenerate m-dimensional variety. Assume either char(K) = 0 or char(K) > deg(X). Here we prove that all general 0-dimensional sections of X containing a tangent vector to a smooth point of X are protectively equivalent if and only if n ? m + 1 ≤ deg(X) ≤ n ? m + 2. 相似文献