全文获取类型
收费全文 | 12235篇 |
免费 | 491篇 |
国内免费 | 221篇 |
出版年
2023年 | 112篇 |
2022年 | 146篇 |
2021年 | 240篇 |
2020年 | 232篇 |
2019年 | 289篇 |
2018年 | 332篇 |
2017年 | 168篇 |
2016年 | 219篇 |
2015年 | 265篇 |
2014年 | 522篇 |
2013年 | 686篇 |
2012年 | 337篇 |
2011年 | 472篇 |
2010年 | 460篇 |
2009年 | 526篇 |
2008年 | 652篇 |
2007年 | 552篇 |
2006年 | 471篇 |
2005年 | 438篇 |
2004年 | 392篇 |
2003年 | 357篇 |
2002年 | 286篇 |
2001年 | 196篇 |
2000年 | 203篇 |
1999年 | 204篇 |
1998年 | 217篇 |
1997年 | 193篇 |
1996年 | 176篇 |
1995年 | 176篇 |
1994年 | 178篇 |
1993年 | 153篇 |
1992年 | 153篇 |
1991年 | 131篇 |
1990年 | 124篇 |
1989年 | 129篇 |
1987年 | 107篇 |
1986年 | 114篇 |
1985年 | 127篇 |
1984年 | 182篇 |
1983年 | 123篇 |
1982年 | 152篇 |
1981年 | 145篇 |
1980年 | 164篇 |
1979年 | 168篇 |
1978年 | 162篇 |
1977年 | 152篇 |
1976年 | 197篇 |
1974年 | 107篇 |
1973年 | 260篇 |
1972年 | 139篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Meloidogyne mayaguensis n. sp. is described and illustrated from specimens obtained from galled roots of eggplant, Solanum melongena L., from Puerto Rico. The perineal pattern of females is round to ovoid with fine, widely spaced striae. It has occasional breaks of striation laterally and a circular tail tip area lacking striae. The stylet, 15.8 μm long, has reniform knobs that merge gradually with the stylet shaft. Males have a high, rectangular, smooth head region, not set off from the body contour. The labial disc is continuous with the medial lips which do not slope posteriorly. The styler, 22.9 μm long, has large rounded backward sloping knobs; the shaft is of uneven diameter. Mean body length of second-stage juveniles is 453.6 μm. The truncate head region is not annulated, and the rounded, slightly raised labial disc and the crescentic medial lips form dumbbell-shaped lip structures. The stylet, 11.6 μm long, has rounded, posteriorly sloping knobs. The slender tail, 54.4 μm long, gradually tapers to a bluntly pointed tip. Tomato, tobacco, pepper, and watermelon are good hosts; cotton and peanut are not hosts. M. mayaguensis n. sp. reproduces by mitotic parthenogenesis and has a somatic chromosome number of 2n = 44-45. The enzyme patterns are unique among Meloidogyne species. 相似文献
82.
Tylenchulus graminis n. sp. and T. palustris n. sp. are described and illustrated from broomsedge (Andropogon virginicus L.) and pop ash (Fraxinus caroliniana Mill.), respectively. T. graminis resembles T. furcus in having a distinct anus, but T. graminis second-stage juveniles (J2) do not have a bifid tail. T. semipenetrans does not have a perceptible anus. The mature female of T. graminis has a mucronate pointed terminus while T. semipenetrans has a smooth and round terminus. T. graminis males have wider stylet knobs and basal bulb and a longer tail than T. semipenetrans males. T. graminis J2 have a longer posterior body portion (without large fat globules) than T. semipenetrans J2. T. palustris resembles T. semipenetrans in having an undetectable anus but differs by the short and conoid mature female postvulval section. The male of T. palustris has larger stylet knobs and basal bulb than those of T. semipenetrans and a bluntly rounded tail terminus, which is tapered in T. semipenetrans. T. palustris differs from T. furcus and T. graminis in having an undetectable anus, by the conoid postvulval section of mature females, by the shorter and rounded tail of males, and the shorter J2 posterior body section without large fat globules. T. graminis and T. palustris are parasites of indigenous flora of Florida. 相似文献
83.
Summary Ring formed actin filaments were observed in tobacco BY-2 cells. The change of this structure during culture was followed by fluorescence microscopy. 相似文献
84.
85.
棕色固氮菌固氮酶FeMo蛋白与过量(5-6个当量)的酸性靛蓝保温30-60分钟后,蛋白中的P-金属原子族全部氧化,然而蛋白中的FeMoCo全都处于还原状态。Na2S2O4使这种部分氧化的FeMo蛋白中的P-ciuster重新不,甲基紫精可加快这种还原,而亚甲蓝等氧化剂则使这种蛋白中的FeMoCo受到氧化,对这种部分氧化的FeMo蛋白分别进行CD还原滴定和测定氧化过程中的EPR/ABS的变化已经得到p-Cluster和FeMoCo的氧化还原当量数目。 相似文献
86.
Intramolecular localization of epitopes within an oligomeric protein by immunoelectron microscopy and image processing 总被引:1,自引:0,他引:1
N Boisset J Frank J C Taveau P Billiald G Motta J Lamy P Y Sizaret J Lamy 《Proteins》1988,3(3):161-183
Three epitopes have been localized by immunoelectron microscopy on subunit Aa6 of the 4 x 6-meric hemocyanin of the scorpion Androctonus australis. Soluble immunocomplexes composed of monoclonal antibodies and of native hemocyanin were purified, negatively stained with uranyle acetate by the single-layer technique, and examined under the electron microscope (EM). The molecule images were digitized, aligned, and submitted to correspondence analysis according to the method of Van Heel and Frank (Ultramicroscopy 6:187-194, 1981). A high-precision localization of the attachment point of the Fab arm to the antigen was achieved through a careful analysis of the average images. This method easily allowed the discrimination of epitopes located in different domains (Mr 20 kDa) of the same subunit. Nonoverlapping epitopes located in the same structural domain of subunit Aa6 could be distinguished by the stain exclusion patterns of their Fab arms. The method is general and may be used for epitope mapping in any antigen producing definite EM views. 相似文献
87.
Summary Two winter wheat genotypes (Diószegi 200 and Mv 15) were compared for their in vitro androgenic capacity. On average, the induction frequency of embryogenic structures was 71.7% in Diószegi 200 and only 4.3% in Mv 15. The haploid induction ability of the two genotypes differed considerably, with Diószegi 200 being much higher. The difference in the in vitro inductability of the microspores may result from genetic differences which are manifested in the survival rate of the microspores during the culture period and their adaptability to in vitro conditions. Special DNA fluorochrornes were suitable for studying the different pathways of in vitro androgenesis. Our data indicate that the repeated equal divisions of the microspore nucleus might lead to pollen embryo formation, and subsequent divisions of the vegetative portion of the pollen grain after the first asymmetric microspore mitosis can result in pollen callus formation. 相似文献
88.
鲤鳃表面结构扫描电镜研究 总被引:31,自引:0,他引:31
鲤的鳃丝表面显示了由三边形一六边形不等的表皮细胞,呈现出各种图案式的结构。 相似文献
89.
Using high magnification Nomarski interference microscopy a series of optical sections has been obtained through flagellated cells of several green algae in an attempt to establish the absolute orientation of their basal bodies. Using this technique we have confirmed that in Spermatozopsis similis basal bodies are displaced into the 1/7 o'clock position, whereas in gametes of Enteromorpha linza, and zoospores of Trebouxia erici basal bodies are displaced into the 11/5 o'clock position. In addition we report for the first time that in zoospores of Microthamnion kuetzingianum basal bodies are also displaced into the 11/5 o'clock position. Basal body absolute orientations can thus be determined by light microscopy and do not require serial section electron microscopy. The method should be useful for class-level recognition of unknown green algae at the light microscope level. 相似文献
90.
Philippe Fragu Colette Brianon Catherine Fourr Jrme Clerc Odile Casiraghi Josette Jeusset Frdrique Omri Sylvain Halpern 《Biology of the cell / under the auspices of the European Cell Biology Organization》1992,74(1):5-18
We attempted to indicate the requirements for biomedical applications of SIMS microscopy. Sample preparation methodology should preserve both the structural and the chemical integrity of the tissue. Furthermore, it is often necessary to correlate ionic and light microscope images. This implies a common methodological approach to sample preparation for both microscopes. The use of low or high mass resolution depends on the elements studied and their concentrations. To improve the acquisition and processing of images, digital imaging systems have to be designed and require both ionic and optical image superimposition. However, the images do not accurately reflect element concentration; a relative quantitative approach is possible by measuring secondary ion beam intensity. Using an internal reference element (carbon) and standard curves the results are expressed in micrograms/mg of tissue. Despite their limited lateral resolution (0.5 microns) the actual SIMS microscopes are very suitable for the resolution of biomedical problems posed by action modes and drug localization in human pathology. SIMS microscopy should provide a new tool for metabolic radiotherapy by facilitating dose evaluation. The advent of high lateral resolution SIMS imaging (less than 0.1 microns) should open up new fields in biomedical investigation. 相似文献