全文获取类型
收费全文 | 2141篇 |
免费 | 193篇 |
出版年
2023年 | 16篇 |
2022年 | 7篇 |
2021年 | 60篇 |
2020年 | 51篇 |
2019年 | 58篇 |
2018年 | 46篇 |
2017年 | 42篇 |
2016年 | 87篇 |
2015年 | 158篇 |
2014年 | 133篇 |
2013年 | 146篇 |
2012年 | 199篇 |
2011年 | 170篇 |
2010年 | 91篇 |
2009年 | 75篇 |
2008年 | 115篇 |
2007年 | 98篇 |
2006年 | 98篇 |
2005年 | 61篇 |
2004年 | 70篇 |
2003年 | 52篇 |
2002年 | 69篇 |
2001年 | 31篇 |
2000年 | 32篇 |
1999年 | 34篇 |
1998年 | 16篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 17篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 26篇 |
1991年 | 12篇 |
1990年 | 18篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 20篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 19篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 5篇 |
排序方式: 共有2334条查询结果,搜索用时 140 毫秒
1.
2.
The Wageningen Delivery of Functionality symposium covered all aspects involved with food structural design to arrive at high-quality
foods which meet demanding customer expectations and regulatory requirements. The symposium integrated aspects from the structural
organization of foods at molecular and supramolecular scales to dedicated techniques required to describe and visualize such
structures, the gastro-intestinal events and how to model these in a laboratory setting, and finally the impact those food
structures and ingredients have on the consumer’s physiology and on the human perception. As an interdisciplinary platform,
bringing together more than 160 researchers from academia and industry, the symposium meanwhile fulfills an important role
in the food science community. 相似文献
3.
Ewa A. Czy Carla Guilln Escrib Hendrik Wulf Andrew Tedder Meredith C. Schuman Fabian D. Schneider Michael E. Schaepman 《Ecology and evolution》2020,10(14):7419-7430
- The growing pace of environmental change has increased the need for large‐scale monitoring of biodiversity. Declining intraspecific genetic variation is likely a critical factor in biodiversity loss, but is especially difficult to monitor: assessments of genetic variation are commonly based on measuring allele pools, which requires sampling of individuals and extensive sample processing, limiting spatial coverage. Alternatively, imaging spectroscopy data from remote platforms may hold the potential to reveal genetic structure of populations. In this study, we investigated how differences detected in an airborne imaging spectroscopy time series correspond to genetic variation within a population of Fagus sylvatica under natural conditions.
- We used multi‐annual APEX (Airborne Prism Experiment) imaging spectrometer data from a temperate forest located in the Swiss midlands (Laegern, 47°28'N, 8°21'E), along with microsatellite data from F. sylvatica individuals collected at the site. We identified variation in foliar reflectance independent of annual and seasonal changes which we hypothesize is more likely to correspond to stable genetic differences. We established a direct connection between the spectroscopy and genetics data by using partial least squares (PLS) regression to predict the probability of belonging to a genetic cluster from spectral data.
- We achieved the best genetic structure prediction by using derivatives of reflectance and a subset of wavebands rather than full‐analyzed spectra. Our model indicates that spectral regions related to leaf water content, phenols, pigments, and wax composition contribute most to the ability of this approach to predict genetic structure of F. sylvatica population in natural conditions.
- This study advances the use of airborne imaging spectroscopy to assess tree genetic diversity at canopy level under natural conditions, which could overcome current spatiotemporal limitations on monitoring, understanding, and preventing genetic biodiversity loss imposed by requirements for extensive in situ sampling.
4.
5.
I Fabian Y Kletter I Bleiberg 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1987,185(4):434-440
The modulatory effect of 1,25-dihydroxyvitamin D3 (vit D) on the growth of myeloid progenitors and on the composition of the stromal layer in human bone marrow long-term cultures was studied. Vit D (2 X 10(-8) M) caused an enhancement in myeloid progenitor cell (CFU-C) growth in the nonadherent and adherent layers during the entire 5-week incubation period. The vitamin did not alter the differentiation pattern of CFU-C (monocyte-macrophage progenitors CFU-M, granulocytic progenitors CFU-G, or monocyte-granulocyte progenitors CFU-GM). Vit D caused a marked increase in the percentage of lipid-containing cells in the adherent layer and an increase in the number of cells that specifically bound My4 monoclonal antibody (McAb), that reacted positively to fluoride-sensitive alpha-naphthyl acetate esterase, and that phagocytosed Candida albicans (CA). Concentrated supernatants harvested from control cultures showed significant levels of myeloid colony stimulating factor (CSF) activity. The addition of vit D to cultures for 5 weeks did not alter CSF levels. These results suggest that vit D may play a role in hematopoiesis by acting directly on the progenitor cells or via the stromal cell production of stimulatory factor(s). 相似文献
6.
J C van der Linden C J Herman J G Boenders M M van de Sandt J Lindeman 《Cytometry》1992,13(2):163-168
Studies concerning flow cytometric assessed DNA content reveal problems in interpretating DNA histograms of tumor specimens. The main problems are histograms with a broad coefficient of variation in the G0/G1 fraction; a high G2M fraction and samples with a low percentage of tumor cells. Therefore, in the present study, 382 fresh tumor specimens of carcinomas were analysed routinely, double labeled with, on the one hand, propidium-iodide for assessing DNA content and, on the other, a monoclonal keratin-antibody for marking epithelial and tumor cells. Of the 311 tumor samples, using single parameter analysis 165 (54%) were classified as DNA aneuploid and 146 (46%) as DNA "euploid." By double parameter analysis, 224 (72%) samples were keratin positive and 87 (27%) keratin negative and, of the 224 keratin positive tumors, 175 (78%) were DNA aneuploid and 49 (22%) DNA euploid. The DNA histograms of single and double parameter analysis were compared and it was concluded that in 24 cases (11%) keratin labeling was necessary to recognize DNA aneuploidy. In another 23 (10%) cases, keratin labeling was helpful in assessing DNA aneuploidy. Finally when the results of the 311 samples were combined, 215 (68%) were scored as DNA aneuploid and 99 (32%) DNA euploid. Thus the overall gain in assessing DNA aneuploidy using the double labeling technique is 14%. In conclusion, it is shown that keratin labeling on fresh tumor cell suspensions of epithelial tumors is of additional value in establishing DNA content. Because single parameter DNA assessment is adequate in approximately 60% of the tested samples, the double labeling technique can be performed routinely, or after initial single parameter DNA assessment. Histograms having a broad CV and/or a high G2M are good candidates for the double labeling technique. Using this technique, DNA-content assessment becomes more reliable. 相似文献
7.
Adriaan P. de Bruïne Winand N. M. Dinjens Margriet M. J. Pijls Edith P. M. v. d. Linden Mat J. M. Rousch Peter T. Moerkerk Antony F. P. M. de Goeij Fred T. Bosnian 《Virchows Archiv. B, Cell pathology including molecular pathology》1992,62(1):311-320
In colonic neoplasms, endocrine differentiation is encountered not only in carcinoid tumors but also in adenocarcinomas, where
endocrine cells may represent a distinct line of differentiation in the tumor. The significance of endocrine differentiation
in colorectal cancer is not well established, partly because of the paucity of tumor cell lines which can serve as a model
for studying endocrine differentiation. In this report we describe the properties of NCI-H716 cells, a cell line derived from
a poorly differentiated adenocarcinoma of the caecum, under various in vitro conditions and as xenografts in athymic mice.
Phenotypical properties were immunohistochemically assessed using a panel of differentiation related antibodies, and also
by Northern blot analysis and by electron microscopy. Receptors for biogenic amines and peptide hormones were analyzed by
ligand binding assay. These studies show that:
相似文献
1. | NCI-H716 cells can be undifferentiated, or show endocrine, mucin-producing or “amphicrine” properties. |
2. | Endocrine differentiation of NCI-H716 cells preferentially occurs in xenografts in athymic mice, which suggests that mesenchymal elements induce endocrine differentiation. |
3. | NCI-H716 cells express large amounts of high affinity receptors for gastrin, serotonin and somatostatin and these substances can regulate growth. Thus, NCI-H716 cells form a suitable model for the study of endocrine differentiation in intestinal epithelium and of auto- or paracrine growth regulation in intestinal neoplasia. |
8.
Linden Higgins 《Journal of Insect Behavior》1992,5(5):635-655
Individuals of the orb-weaving spider Nephila clavipesbuild complex webs with a region used for prey capture, the orb, and tangle webs opposite either face, the barrier webs. Barrier webs have been hypothesized to serve a variety of functions, including predator defense, and the primary function of the barrier web should be reflected in the relative size of the barrier to the orb under varying conditions of foraging success and predation risk. To investigate the effects of predation pressure and foraging success on barrier web structure, I conducted a comparative study in three disjunct populations that differed in predation risk and foraging success. Although both the orb web and the barrier webs are silk, there was no indication of a foraging-defense trade-off. Barrier web structure did not change during seasonal shifts in orb web size related to changes in preycapture rate, and barrier web silk density and orb radius were positively correlated. The hypothesis that the construction of barrier webs is in part a response to predation pressure was supported. Barrier webs do deflect attacks by some predators, and barrier webs built by small spiders, suffering frequent predation attempts, had a higher silk density than barrier webs built by larger individuals. Additionally, barrier web complexity decreased at a later age in areas with higher predation risk. 相似文献
9.
Ming Shiang James C. Linden Ali Mohagheghi Karel Grohmann Michael E. Himmel 《Applied microbiology and biotechnology》1991,34(5):591-597
Summary Fed-batch fermentations of Acidothermus cellulolyticus utilizing mixtures of cellulose and sugars were investigated for potential improvements in cellulase enzyme production. In these fermentations, we combined cellulose from several sources with various simple sugars at selected concentrations. The best source of cellulose for cellulase production was found to be ball-milled Solka Floc at 15 g/l. Fed-batch fermentations with cellobiose and Solka Floc increased cell mass only slightly, but succeeded in significantly enhancing cellulase synthesis compared to batch conditions. Maximum cellulase activities obtained from fermentations initiated with 2.5 g cellobiose/l and 15 g Solka Floc/l were 0.187 units (U)/ml, achieved by continuous feeding to maintain <0.1 g cellobiose/l, and 0.215 U/ml using the same initial medium when 2.5 g cellobiose/l was step-fed after the sugar was nearly consumed. In batch, dual-substrate systems consisting of simple sugars with Solka Floc, substrate inhibition was evident in terms of specific growth rates, specific productivity values, and maximum enzyme yields. Limiting concentrations of glucose or sucrose at 5 g/l, and cellobiose at 2.5 g/l, in the presence of Solka Floc, yielded cellulase activities of 0.134, 0.159, and 0.164 U/ml, respectively.
Offprint requests to: M. E. Himmel 相似文献
10.
The histological inspection of tumor tissue for the purpose of reporting a tumor grade is a problem of significant clinical importance. The grading by a pathologist is only partly reproducible due to vaguely defined, subjective criteria. In this article we describe and evaluate a set of measurable features that quantitate the differences in tumor tissue. Different aspects of the reproducibility of the measurements under varying conditions of image selection, focus, and noise have been investigated. Three hundred thirty-three images were digitized from 111 bladder tissue sections (4 microns thick, Feulgen stained), using the ICAS microscope-camera platform. A segmentation routine was developed to segment the images into nuclei and background without any user interaction. Size, shape, optical density, and texture features were measured on and among the objects found by this segmentation routine using the image analysis package Acuity. The results of the measurements showed that there is a significant quantitative difference between grade 1 and grade 3 tumors. Grade 2 tumors can be described as "in between grade 1 and grade 3" and falling somewhere on an increasing scale between grades 1 and 3. Grade 2 tumors do not seem to represent a statistically distinct population. The procedure described here is shown to be quite reproducible in the presence of noise, reasonably reproducible in the event of a modest amount of defocusing (with grade 3 tumors exhibiting the most sensitivity), and less reproducible in the context of which fields-of-view are chosen for analysis. 相似文献